The needs of the few would deny the needs of the many.
Though this item would be loved in upper levels where there aren't any shitty ADCs, in Bronze where shitty ADCs are common it would be hated. It would also only be loved by certain supports (Leona, Thresh, Braum) and not others (Lux, Annie, Karma).
Supports like the first group don't need many items. The gold generation passive and assists are plenty for them. They build cheap defense and support items that don't need much gold. Supports in the second group need to build like mages to be effective, especially in the laning phase. Feed a Lux support in the laning phase and watch her keep you at low health with constant poke.
This is especially true in Bronze and Silver, where the likelihood of getting a bad player as your ADC is high. Though the enemy team probably has a bad player as well, you still need to be able to capitalize on their errors while mitigating your own. A shitty Vayne without items is going to run into teamfights and get blown up. A shitty Vayne with items is going to run into teamfights and get blown up.
There's no difference in the damage a shitty Vayne does based on items because they run into the middle of a teamfight and get CC'd and killed. If you're supporting as Lux and you have all the gold from all the kills you're piling up because you don't suck, you can throw your shield and keep that Vayne alive a couple more seconds because you've stacked AP to high heaven. If that shitty Vayne got all your gold because of this support item, you can't do that because you don't have enough AP. The shitty Vayne still does the same damage as before (more time alive with less DPS is still more damage), but you do more damage too.
(Which is why I suggest to all the shitty Vaynes I encounter to build tanky AS.
and the rest defense is more damage with Vayne's W than people realize.)