That's the problem with catering your ruleset to the top players; most generally want as a little change as possible to not jeopardize their chances of winning, and don't want to learn extra stuff to win if they could avoid it. See the MetaKnight ban topic in Brawl, where the most vocal opponents, such as M2K and Zero, were usually top players who played MetaKnight extensively (and that ended up being the undoing of the MetaKnight ban, as the TOs of the biggest nationals kept MK legal to appeal to these players, which then forced everyone else to not keep the MK ban as their players otherwise wouldn't get experience for this vital matchup).
As such, it's a really terrible appeal to authority when people point to "top players don't like them!" as a reason against customs.
Customs were pretty much screwed no matter what happened at Evo. If the top placings consisted of players outside the norm who utilised customs, critics would go "see custom jank is bad for the game as it allowed worse players to win!". If the top placings consisted of the usual suspects, they would go "see customs don't really help the balance, they're not worth the effort!".
The latter ended up happening with customs putting on a good show outside of a couple custom Villagers and Static Manny, and sure enough, "they don't really help the balance anyway" is a prevailing argument against them now.