Welp, they did it - they nerfed most my mains - the whole sub-class of artillery mages, that appear in ARAM at most once every 50 games. Ziggs is basically useless since he is countered by a single MR item. Lux and Xerath are in a similar position, maybe less problematic, since Ziggs is just straight out does 15% less dmg and receives 8% more dmg (as if he wasn't squishy enough). Miraculously, Vel'koz and Jhin, even with nerfs, are good enough (probably because of their passives). Even though Jayce isn't in the list of nerfs, they definitely nerfed him - with the same build he just does less damage.
On the other hand, Master Yi didn't receive any nerfes, yet he always was a power-house in ARAM. Same goes for cc-machine - Leona. Fizz got buffed - why buff someone, who can dodge most of the shit thrown at them via a non-ultimate ability with relatively low CD is beyond my comprehension. Garen always is pretty strong and don't get me started on bloody Hecarim - he even now receives 10% less damage. Combine that with his absurd amounts of damage and nerfs to artillery mages and you get pretty... UNBALANCED ARAM.
So, Riot tried to balance ARAM and in the process, they completely messed it up - when a team of 4 ADCs and Jax all did less damage than Janna (support!!!! if you forgot), then there's no balance.
Also, matchmaking is clearly one-sided - one team will be a bunch of random champions, not capable of making any plays because their kits are mutually exclusive (e.g. Tristana, Neeko, Ryze, Soraka and Zyra) vs. a cc madhouse (Brand, Volibear, Veigar, Diana and Blitzcrank).
Right now ARAM is almost unplayable for some champions, that should be fun to play. These %dmg reduction or increase changes are the worst possible way of trying to balance ARAM.