I was referencing melee as the, "banning stages mostly because of one character isn't something new." Why is it a bad precedent? What would you have done to change the stage rules? You can't just dismiss it because Melee is a different game, because they're very similar with similar game mechanics and the same counterpicking system.
I was saying that if you ban a character from playing on a stage, what about the problem of someone else CPing that stage so their opponent can't use MK? My example being me CPing M2K to a stage on which MK is banned so he can't use MK. Would there be an exception?
And even disregarding that, banning a character from using a stage brings up other problems. For example, if you were to ban MK from using RC or Brinstar it'd be because he's "too good" on the stages, which is an arbitrary distinction, and despite the multiple matches of MKs losing on the stages and proving the stages are cut-and-dry broken for them, they're still banned.
Since you can't measure the amount of "good" MK is on those stages but are banning them exclusively for him anyway, you run into the problem of people wanting to do the same thing for other stages. Falco (and Kirby IIRC) is really good on Japes, much more "good" than what he would be on a neutral stage for him (which, I'm assuming since you support a 9 stage starter it'd be a stage like Yoshi's or something in this example). People could be upset that they have to "waste" a ban on Japes when Falco can still take them to PTAD (used in this example because IIRC you support it) which is still a REALLY good advantage for Falco, or even stages like FD or BF. If he's so much better and arguably "too good" on the stage, people can argue to ban Falco from Japes but not the stage itself.
Which brings problems of other characters, like Diddy and ICs on FD; an argument could be that people shouldn't have to waste a ban on it when both still are really good on BF and SV or PS1, and because those stages are not only "too good" for them but much better for them than their "neutrals", they should be banned. Even in any situation where X character is "too good" on a stage, like G&W on Norfair or Olimar on Mansion (side note, would much rather play an MK on brinstar/RC/norfair than these characters on these stages lol), people would argue for a ban only for the character because, well, you already did it for MK with some stages, why can't you do it with other characters?
Oh yeah, there's also the issue of not only banning MK from those stages. Do you only ban MK from RC/Brinstar/Norfair when other characters (like Wario on Brinstar, and G&W on Norfair) all get just as good buffs if not better ones from the stages? What about certain match-ups? D3 on RC is really dumb for some match-ups but fine for others.
"Too good" is too undefined to restrict certain characters from using the stage. The stage should be broken for it to be banned. Now, if one character clear cut broke a stage but it was perfectly fine for everyone else, it'd be a different story and not letting that character pick the stage is more realistic. But not only does that only work in theory, since realistically for a character to break a stage there have to be quite a few problems with it anyway, but MK doesn't break any of these stages. He just does well on them, and being the best character, he's going to be even better on his CPs.
A more realistic reason why Norfair is banned in most places and Brinstar banned in some is because MK does really well on them, and they aren't the best stages even without that. People can argue that Norfair should be banned even without MK, and I've heard arguments that Wario gets huge buffs on Brinstar to the point where banning it isn't so ridiculous. I don't really agree with banning them, but the stages have problems other than MK.