I doubt Vayne will stay up there for much longer. A combination of a high gold income allowing champs to reach their item spike faster + the fact that supports are controlling the botlane due to high damage + the overheal relic meta is allowing Vayne to dominate rn. Her garbage early game is mitigated by the fact that she can afk with overheal + relic and allow her support to carry the lane and then reach her item spike super quickly and carry the game.
As much as everyone hates it though I'm glad she's in meta. Every time she isn't she's always trash tier cause her early game is too weak.