And so you're saying that without customs, people won't exploit the best parts of their character and make that what their meta revolves around?
Mac is a bad/extreme example though. Why exactly are we trying to balance the game around Mac? Are we about to ban Duck hunt just because Mac does poorly on it? There has to come a point where people say, you know what, maybe this is just a bad character.
Customs are fairly balanced in their own way; for every pro there is a con (it's just that sometimes that con is not immediately obvious, or people find ways to circumvent the con). My understanding of the recent tournament is that the stalling Villager tactics didn't work on competent players that adapted to it, and this was the first time they had encountered it; and you know, there is a such thing as an early metagame which in turn requires a grace period in which people learn, experiment and adapt etc. It's completely foreseeable that some people would be beaten by such tactics so early on. I have someone in my scene that uses customs palutena so I'm fully aware of what she is capable of when you combine lightweight with super speed on a stage with platforms. Yet you don't hear me calling for a ban on customs. Lightweight makes Palutena take more damage and die earlier, so there's a risk involved for her too, and then there is the cooldown to be reckoned with which leaves her a sitting duck, and yes, it can be avoided by refreshing on platforms, but this tactic can be stopped if you're vigilant.
See I don't even think about customs as an addition. Each character has at their disposal certain moves, and those moves (in my mind at least) include the customs just as easily as they would include their default specials. Oh but you have to unlock them so they are therefore treated differently? How about unlockable characters?
The game wasn't balanced with the competitive community in mind anyway, which is why slower characters will always suffer in the long run, so why are we worried about the game developer's idea of balance?
I've already said that the 'time' to set up customs is not a big deal at all. It's so small that it's not even a point that can be made. We didn't make a big deal about people setting up custom controls in Brawl, and that takes way way longer.