I need customs because I main MegaMan and he's terrible without them. Skull barrier is a godsend and the explosive bubble is much better than the default side B. His tornado recovery opens up so many offensive options; it's the combo starter everyone needs. Of course you never want to replace metal blade though.Smash may not need customs to thrive, but that doesn't take away that it still benefits greatly from their presence, at least in my opinion.
Yeah, some customs should probably be banned, but the fact that they can greatly improve otherwise unviable characters just makes them too good to ignore.