It's true. Some champs just won't work in higher elo, for their balance point is uncoordination, something not lacking the higher you go. Mostly pick assassins/fighters/bruisers, who job is to catch someone out, which is a mistake not often made in higher games.
They can't really be buffed or nerfed, because they'll either be pick or ban in high elo, low elo pubstompers, or just completely unviable.
Such champions usually get reworked into something more able to be balanced for all skill levels. Fiora is finally getting a rework soon, so maybe she can be a strong LCS pick without being even more of a pubstomper than she is now.