Full tanks are currently mostly unplayable in league. Tried it with Shen, Mundo, Rammus, Amumu (being the exception here, because the ult is still OP, but amumu suffers from the same problems). Not talking about bruisers here, full tanks are in my opinion champion that don't rely on dealing damage at all, just being unkillable and providing CC/Buffs/Utility. That "fantasy" of being the immortal slow dude providing a frontline for your team is dead in league right now.
The problem is not only that bruisers are overall more effective than full tanks because they can kill stuff on their own while full tanks cannot. That would be fine with me, needing teammates to kill stuff. That's what a full tank is built around, after all.
The real problem in my opinion lies in the multiple tank-killer mechanics that Riot has introduced over the past couple of years:
1. Many champions have in-built %HP-dmg mechanics now. Remember when Vayne was the only real tank-killer in game? She was but had a few drawbacks to compensate for that compared to other adcs. But look at the current champion pool: Vi, Zed, Fizz, Gnar, Kog, Yasuo (Arpen). All of these have free built-in tank killer mechanics.
2. Arpen is too commonly used. Last Whisper is a standard item in every ADs build path. You build it regardless wether the enemy built much armor or not because it is just too effective once you have a decent amout of AD. It should be less effective AD-wise and more of a specialized anti-armor item and there should be other interesting AD items to compensate for that.
3. BotrK. This item is so good, every champion relying on fast AA or On-Hit mechanics will definitely buy this while it should also be a situational tank-killer item choice instead of a "meh i'll buy it anyways". So you get an average of 2-3 BotrK in every team. Many champs, like Jax and the likes, tend to buy it as first item regardless of the matchup, an indicator that something went seriously wrong with the design of that item. Making it scale well with the also too commonly used OP Arpen makes it even more flawed.
When I try a full tank and play at least average until midgame, I expect to be a viable frontline for my team, soaking damage while engaging. Hell I was so wrong. Full tanks get mauled by the enemy team in less than 2s, while all they do is AA and using low-CD spells. That's not how it should be. Bring back the tanks, Riot!
tl;dr %HP-dmg and Arpen is too common in league right now while it should instead be an anti-tank OPTION. Regardless of that, you see multiple BotrK and Last Whisper every game, while some champs have even more built-in tank-killer mechanics. Fix that. Bring back the full tanks.