Before I start, a couple of things:
a) This is meant to be a feedback for Riot, really really REALLY not a pointless/endless discussion with a guy that "OMG I have a 57% win rate with her U DON'T UNDERSTAND!11!", another one that "I swear I know a streamer that said she is a sleeper OP!1" and so on. For one thing that is not the point (more on that very soon), for another is a...feedback. Feel free to comment etc ofc, but keep in mind that.
b) This is NOT about Sejuani strength. I will address that part too briefly I guess but that's NOT the main point at all. The point will be how her kit feels, how much is FUN, basically. May be seem otherwise at the start but if u will keep reading (but why u should want to?) u will see were I wanted to go.
c)English is not my native language so the post will be likely hard to follow sometimes. Grind your teeths or just give it a pass, unless u work for Riot.
So, I have mained Sejuani for MANY years now, basically since her release.
I have MANY MANY thousands of mastery points over my accounts with her, was my "to go" pick when I still did ranked and so on, I really know the old one well.
Up until the recent rework Sejuani was relevant in the meta for very few weeks, many years ago; was buffed or w/e (don't remember exactly how) and she become a strong pick.
Riot reacted to that by nerfing her, and then nerfing her again and then...u get the idea.
When the last nerf was seen in PBE basically EVERY streamer, pro etc said the same thing: "This is absurd, is an over nerf so big it will kill her completely". Didn't required a genius to figure that out tbh: was SO clear was too much that my conclusion was "Meh, Riot WANT her to be out of the meta for some reason".
I shrugged and moved on, keeping playing her happily: wasn't SO bad to be unplayble, she was still very fun to me so I didn't cared that much; I didn't understood why Riot wanted that (I know is its policy to leave a champ on the weak side if is somehow "toxic" but that didn't seemed Sejuani case AT ALL), but I ultimately didn't cared THAT much.
Years later, Riot announced a Seju rework, explaining why was needed: the old Seju, basically, was a "walking ultimate".
I think this was a BIG misinterpretation of the champ by Riot, and I'll explain why.
I can certainly see the logic behind it: "Sejuani rely very much on her ult, without it she can't do much etc"; true to an extent, but not for the reasons Riot though.
The plain truth was that the old Seju early game was ATROCIUS, SUPER bad.
She struggled hard in basically every aspect, was prone to be bullied by other junglers yadda yadda yadda; at lvl 6 she gained her first big power up cause her ult was indeed very good, allowing her to shift from "very weak champ overall" to "very weak champ overall BUT with an ult that can grant some kills etc".
Thing is: Seju at lvl 6 was still quite bad, even with her ult. Cause Seju wasn't about the ult as much as she was about her LATE GAME.
That's the main thing: Seju mid game was more than fair (is she managed to do ok), her late was VERY strong potentially; and that's not cause of the ult, at least not MAINLY cause of it.
Seju was a tank designed for tf, to go in the enemies face and CC them, peel for the carries etc; she needed the items, the tankiness to be able to do so and the right situations (not likely to happens in the early game).
For example, a Seju late game WITHOUT her ult was still much, MUCH stronger than a Seju early game with it, without any doubts; her kits and cd still allowed her to dish out lot of hard/soft CC in a tf of average lenght and be a true asset for the team.
I am denying the strenght of old Seju ult? Not at all, was a very strong one. But, like everything, an ult can be very strong AND overrated at the same time.
Seju ult was designed for tf, had good synergy with her and was surely a "potentially tf changing one"...like many, MANY other ult.
Malphite (a champ that is WAYYY more ult dependent than the old Seju ever was; to think that she was reworked cause "she rely too much on her ult" while him still exist is honestly a joke) has an ult that is way better in almost every situation: anti cleanse, anti qss, easier to land (in many situations was tricky to land Seju ult in a way to maximize its effects), Amumu ult is much easier to land and still very strong yadda yadda yadda.
a) Seju didn't rely on her ult more than those champs, in fact a lot less in some cases (Malphite, but i'd rather go with a Seju without ult than an Amumu without it all day, i'll prolly avoid every tf with a Kennen without the ult and so on, just to quote some champs with "similar" ulties.
b) Seju ult wasn't stronger than those kinda ults.
He had his advantage (big casting range, Amumu need to be closer or hit his Q to engage), his flaws (skillshot, u need to predict how it will shatter, MANY times u won't hit everyone), but wasn't nothing above the powerlevel of many, many, MANY other ultimate, and below some of them (Malphite, again), wasn't something even close to "totally define her" (Malphite...again?) like Riot stated.
TL DR: Seju main problem was her ABYSMAL early game, that could destroy her in same cases.
Gaining access to her ult was a nice power spike but mainly cause before it she was SO weak that every relevant "power up" felt like a blessing. And, anyway, her time to shine was meant to be late game thx to the OVERALL design of her kit, that allowed her to be MUCH more than an "ult bot".
All in all, I feel Sejuani was a bit underrated.
Was surely on the weak side (a very bad early is a MAJOR flaw in a jungler) but many players didn't know just how strong she could become late game. I still think that a moderate buff (nothing too special, some early game love) would have pushed her in the meta at least as a "decent" pick, and ofc that's what I think Riot should have done if the idea was to help her.
Now, let's address the NEW Seju kit.
First of all, the ult is very, VERY bad.
A single target skill shot that stun for 1-2 second and deals very little damage is basically a joke, even with the added bonus of the "slowing zone" and feels very, very underwhelming. The problem is not even that is a weak ult, the problem is that it feels very lame and unfulfilling, a capitol sin for an ultimate.
Even if the idea was to redirect some of Seju power into the other skills they took that waaay to far, to the point were the ult doesn't feel "special" or "exicting" or...fun at all, just a random skill that, with some adjustments, could very well be a basic skill for another champ.
That's, in my book, is the first BIG mistake.
An ultimate should always feels as an ultimate, especially an ultimate of this kind (stuff like Singed ultimate etc are a bit of a different story); no matter your reasons if u fail there u did something wrong.
Moving to the rest of the kit, the big nerf on the Q (u can't knock up more than one champ anymore) and the AoE replaced with a very meh W with a clear main purpose (helping racking up stacks for the E) mean basically that now Sejuani is very "E" centered, IMO much more "E" centered of how much the old one was "ult centered".
Half of her strength rely now in the ability of stunning enemies with her E during a tf and that's very sad, for the simple fact that her E is not designed very well.
First of all the "stack meter" is not very visible/clear and, during a convoluted tf can happen to be hard to tell who is ready to be stunned; may seems a nit pick but those skills heavily rely on the player being able to immediately "read" them and with Seju E is not always easy.
The big problem, tho, lie in the core mechanic: u gain stacks hitting enemies or...if nearby **MELEE** allies hit them. On the surface seems quite similar to Braum passive, but that's not the case, at all.
Restricting the stacking to melee champs only means that either your allies pick around your Seju to help her be useful (quite absurd and not realistic in 90% of the games) or that u need to cross your fingers hoping that u will have luck, cause usually u can count on one, MAX two other melee champs to help you out, and that's pretty much the best case scenario.
Being like that, Seju E require insane coordination with your melee allies. With Braum u hit a guy and the whole team get a simple information "hit him again a bit and he will be stunned, easy as pie", with Seju the melee allies are left wondering if is really worth trying to go for that guy with a stack on, cause many times is still a gamble, many others can be very dangerous to even try cause while a Braum stun takes very little time to be proc, Seju E require on average much more time, taking into consideration that u still need to active it after the full stacks, and that's not a small difference.
So, all that the new Sejuani can do in a tf is desperatly try to land a good W only for the sake of her E (and, btw, a skill basically only useful in combat to enable the use of another skill is not very exciting...), knowing full well that, most of the time, she will NEED the help of her allies to get something done.
About the "need for help" btw: yeah, LoL is a teamgame etc, very true. But except in LCS and in full premade, serious teams, you cannot expect a very good level of coordination (I saw countless time very bad team coordination even in master/challanger solo Q), u cannot expect half of your team to always be at your service for the sake of your E, considering that during the average TF every champ has a LOT to think/do besides "uh I must be sure to watch every stack meter of the enemy and rush to the first stunnable to help my Seju! <3 ", considering that sometimes could be the right move but the ally didn't realize it etc.
To summarize, new Sejuani rely wayyy too much on his E, her kit is way too "E centered" and she need to rely too much on others, for a skill that, frankly, often ask just too much to Seju allies.
To use her E well (and if she can't use it well is useless GARBAGE) most of the time she NEEDS the help of other champs and, frankly, sucks a lot to play a champ that can't do what is supposed to do alone, that need cooperation to use her own skills, that can be played PERFECTLY and still not be able to be impactful if your team is unable/incapable of coordinate with u.
To conclude, I think Riot botched her reword very hard.
First and foremost a rework wasn't really needed (just a buff if the goal was to make her relevant again), second her new kit is messy and not fun at all.
A lame ultimate, a nerfed Q and a "ehy I will help you use your good skill!" W left everything on the shoulder of a E that often feels very clunky, with a "stack meter" that is a pain to track in a big tf and an experience that, overall, is just not very fun.
Running in the field desperately trying to rack up stacks 24/7 during teamfights feels like more of a chore than something actually exciting, to the point that I have gave up on her after some games: not cause she wasn't strong as I wanted (who cares, I played her for years and years when was clearly on the weak side), because she was waaaaaaaaaay less fun than she was before, with uninspired mechanics and without a clear identity.
Btw, I think she will be a failure even strength-wise: her kit is very bad, and when a kit is bad a champion become a pain to be balanced, cause u need to give him/her insane value, ending making him/her OP, forcing a following nerf and so on and on. After the initial nerfs I already NEVER see her at any level and I think she will stay in that state ("useless until her numbers are buffed enough to make her OP, then nerfed again cause of it, then ultimately forgotten for good"), making the whole picture even worse.
I sure I will miss my lovely boar, and I know a rework can't be reversed (for many reasons, most of them quite stupid like "can't do that or we will look like idiots") but Riot, pls; keep an eye on her, think about it and maybe, in the future, give her some love (aka "make her FUN" not "OMG I WANT HER OP") with another "rework".
I really hope some rioters will read it, thx.