Vayne is a problem IMO
She may have a tough laning phase but its completely and utterly outweighed by the fact that there is absolutely no way to build against her W and that in her laning phase if she gets 2 auto attacks and a condemn off her W passive allows her to win any trades because against squishy champions it functions like a pop of burst damage. Her W is still balanced around the old Meta Golem Bruiser Era and hasn't really been changed since. A champion with a passive ability that negates any possible way to counterbuild it is in my eyes unhealthy. Is Vayne a huge problem right now. No. Is it a lingering problem that needs to be addressed. Yes.
Vayne already has a enough in her kit lowering her burst on her W will not hurt her int he slightest and honestly changing it to physical damage that scales wont hurt either at least that way we can counter build against it.