Alistar Got Nerfs He Didn't Deserve/Couldn't Afford
His heal was nerfed, and now his ult.
First of all, this new patch as well all know dramatically increased tower damage the longer you are in tower range. This is an indirect nerf to alistar because turret dives are his bread & butter.
This new 20% reduction in early game ult shielding is a huge nerf to alistar. As an all in champ, he can't poke, he can't become a credible threat unless he is in the direct line of fire, at which point he is usually diving full hp enemies. Not being able to tank heavily for the 7 seconds allows the rest of the support lineup to have a significant advantage over him at literally every stage of the lane phase, even during his ult unfortunately. Plus, his early game was never strong to begin with.
His win rate has dropped from 51.6 to 48.7 as a result.
Alistar is not and was not a champion that needed a dramatic nerf. There are supports that completely outclassed him in most matchups, even in the previous patch, such as sona, janna, and zilean.
And still, there are much stronger picks that have gone unnoticed this patch like zyra, blitz, sona, and janna.
Basically, alistars new nerf makes his early game outclassed so much that he cannot do the things that make him viable.