Just because some items are op doesn't means support kits need buffs.
If you nerf all support items alike, then buff the supports that are weaker so supports become balanced, that only means if you end up removing the still op by comparison support items like ardent censer, the supports that used to be op and became balanced after the change will become weak, because they were still abusing the item, even if it had more impact.
This is something riot does a lot: they nerf champions that abuse a specific item and finally they nerf the item, but they don't buff the champions again, instead they leave them to rot for a while. In reality, there's even more implications.
By buffing their kits, you're making them less gold reliant. That would make the op item abusers stronger when winning and weaker when losing, while making the others stronger when losing and weaker when winning. But that was all considering you couldn't build non support items. When you add that into account it gets even more complicated.
By nerfing support items, you're making them more prone to building non support items, so maybe you buff the other supports with their support build in mind, then release it into live and BOOM, those supports are now OP because they're building non support items while having an overpowered kit. So now you have to dial back on the buffs a bit. But now you have supports not building the support items that were designed for them and were considered fun and healthy for the game because they're too weak, so you want to fix that, but you have to backtrack all that was done before. That's why you should always attack the root of the problem.
I realize you most likely also meant to nerf only the support items that are busted, and said the "buff kits" because you're stating that you're displeased with support items being too good in general, so they'd be brought down a bit, while champions buffed a bit. I wouldn't be quick to agree with that, there's reasons for and against, but that could be a discussion between us. However, knowing that you probably meant that, I'm typing this for those who might misunderstand that point, or for you if that's not what you meant.