You want ADCs to not be picked? You'll have to nerf them to the point where it will be harder to find an adc in solo queue than support. Or, you could make reworks like Morde without screwing then up as happened in his case.
Vayne is just guaranteed to be strong in a meta of assassins. Her power level otherwise isn't that much better than the other carries. Also, the removal of ghostblade as an ADC item sharply increased her power. She can now reliably duel enemy ADCs with the combo of a BF and shiv. Before you were taking a relatively large risk by trying to duel a lucian with a ghostblade, but not anymore.
It's really a very complex situation. Ghostblade items got removed, but most carries aren't suit to be able to make a big splash in the early-mid game with crit build. Vayne with Q max can actually do that. Plus she can fight back against assassins, potentially being able to win a duel if she doesn't get 1 shot.
So we're stuck with little to no variety in itemization, little to no variety in champion strength, and from what I've noticed, game impact is very inconsistent. I have seen a Twitch hard carry, literally 1v5, then the next game both carries aren't even 2nd in damage and are contributing little.
More than ever exists the problem of the bot lane not being able to snowball by themselves.