I would agree to the extent casters were not as affected by AC because they have been perfecting 'evasion' tactics since the game's inception.
Look, casters have been powerful for a long time (thank you unlimited mana and solo scaling). But when the shield wall goes down in a group, on elite, they get hit hard too. I haven't seen a spike in runs with casters soloing elite content while everyone pikes since the AC changes. The percentage of players who have a caster who can ACTUALLY solo elite in a full group (i.e., no scaling) is very small. There are many who talk the talk but most do it without being able to walk the walk.