Nerf ADC sustain, not support items
They already had to buff support items so people would play it at all, in addition to the nonsensical autofill function.
ADCs are too strong right now because they survive far too long in a fight, but that's because they can have DD, GA, and PD on top of all of the shielding and healing the support provides. But AP champions don't have that luxury, save for the few who were specifically reworked to fit the new gunblade.
The problem is the high amount of defense on AD items currently, not supports. Giving people less reason to play support is never going to be good for matchmaking.