Why Vayne was boosted more, so she could 1 shot people without any skill?

Vayne was never needing more dmg scaling on q or anything extra... she reached at the point she is a monster not only late game but early as well... in my last match I couldn't kill her with swain (I was fed all game long... I finished match 20/10 and lost it ofc, but not this is the problem) even when I was using all my skills on her and using zhonya? It's normal one champion that is smashing literally tanks to not be able to be killed by mages or assassins (we had yasuo as well) also just because you die faster no matter what you're doing? Ofc that now a lot of Vayne mains will rage but think about it... why boosting champions that are not needing like or even when there are more champions which are rather weak at this point???