it's not the meta and it's not the fact that they're "OP"
they're being compared to champions who were designed to be mages. it's literally that simple.
janna controls movment and positioning, lulu controls fight progression. soraka controls regeneration
it's not their kits it's the free cooldown reduction in items and the 5% from intelligence , free mana from the new mage items and the regen from meditation, and synergy of the windspeakers blessing keystone, and the 3 items that build off of forbidden idol.
in order for a mage hybrid to flourish in the support role they're going to have to play differently because of the mastery tree not being set up in a way that promotes mage crowd control as a valid supporting mechanic - how many morganas take courage of the colossus over something in the middle tree? not many. most want that added 5% cdr for their snare and they just grab thunderlords decree or windspeakers blessing.
it's not their kit. it's the masteries, items, and the opponents they face not being able to adapt as easily..