just stop your bias is showing.
It's okay that midlane mages have over 50% winrate because they are the most popular picks there, but it's also okay for a marksman to have under 50% winrate because some are stronger than others.
Top winrate champs in midlane are 90% AP, most assassins are 51%-50% winrate.
Stop your delusional bias, mages are doing fine, those who are struggling need to be looked at and buffed.
So if their winrates are fine, their playrates are fine, and assassins win rates are also fine, why buff them? Mages cant have the same damage as asssassins, because most mages bring their damage from much much much longer range, and usually it is also coupled with utility, often even game winning utility like in case of oriana.
OP.GG is down but looking at other sites looking from lowest winrate to highest, the only champs who really struggle as AP are ryze and syndra, which both got nerfed in rather recent patches or were hit by the rune changes.
EDIT: also to your hexdrinker comment, yes i agree it should be nerfed and null orb should be adaptive damage, it's only fair - i'll agree on those points, it doesnt change the fact that mages are doing fine as they are now, and are a balanced class.