Riot's AP itemsation went too far.....
Let's be real here, it wasn't really the "AP itemsation" update it was the MAGE itemisation update. AP assassins don't really care too much outside of the nerf to Void Staff and the addition of Spellbinder's (which doesn't even look that great).
But no, really, these items were not thought out properly. Pretty much every new or reworked item has CDR and/or mana on it and the passive which goes along with it perfectly synergises with mages e.g. new Luden's.
Say what you will, but I'd prefer to not be literally 2 shot by an Orianna who presses Q->W and then walks away (or shields herself for 500+ at 1-2 items omegaLUL).
The only problematic item before the changes was Morellonomicon and that's the only item they had to change. Instead Riot decided to fan the flames and made mid lane more mage dominant than ever before.
Mages are fine....until you force them into the meta since they have long range, CC, waveclear and a lot of the time utility.
This is not ok.....
