This isn't fantasy land. In the real world, yaknow, the one that matters, there's a toggle. The option to turn items off is just as justified as turning off customs.
Even then, we'd still have the option to delete the sets. If we couldn't delete the sets, turn them all to just the default moves.
And customs on doesn't include customs off. You still have to fight people using customs if it's on, and you're almost always at a disadvantage if you don't use customs. It's like turning items on and saying you don't need to use them, so then items on includes items off and is strictly better.
We still don't live in fantasy land, so none of that matters.
And characters have spots on the CSS, custom sets do not. Custom sets are custom sets and it's delusional to call them anything else.
EVO's results today would notably imply that you are not at a disadvantage if you don't use customs.
Instead you're at a disadvantage if you don't use Sheik or Diddy.
The upper end of the event had very few customs-users. Abadango didn't use any customs on Pac-Man, and only one on Wario (Speeding Bike). I know he used Shooting Star Bit, but I can't recall whether or not he used Luma Warp.
ESAM used Thunderwave HSB frequently, but there were several cases in which he opted for default Thundershock (HSB is another of those near-pure upgrades though). However, he didn't win, or even come top-4.
Nairo utilized an alternate blaster for Zamus for extra range against Sheik. Lost the matchup anyway, came in 3rd.
I didn't follow Mr R through the tournament, but I believe he was running default Sheik all the way through. He came in 2nd.
The event was won by a default "double-nerfed" Diddy Kong.
Whether for an attempt to sound neutral (despite the obvious ignorance and dislike of customs from several casters, including D1) or whatever else, the commentators seemed convinced that customs did not, in any identifiable way, cause any sort of upset resulting in an undeserved win by a lesser player. So in essence, you actually
don't need to use customs, just like you don't
need to use Sheik. But failure to prepare when the ruleset, terms, and sets have been known for months is literally nothing but willful ignorance with a convenient scapegoat.
-_-
I am aware of the enormous scope of custom moves. That still doesn't change the fact that it is a menu toggle. My response was intended to contrast banning a game mechanic vs. banning something that can be changed outside of gameplay.
As for custom sets being custom sets, what, then, happens to Miis? Customs Off includes every possible combination of Mii up to the limit storable on the console. Not accusing you specifically of doing this, but many players and TOs tend to assume Customs Off == Miis Off, which is not reflective of reality by any menu toggle argument. To say nothing of the functional issues with your "I don't find them fun so I oppose them" stance (ban Sheik pls).