The problem with leaving it to the TO is that most TOs are uninformed and act based off of Knee-jerk reactions.
If a couple people complain about Miis about as much as they'd complain about Little Mac, TOs are likely to ban Miis and say "git gud vs mac".
It's also way more common for TOs to just go off whatever the loudest majority wants, as to not upset anyone. They're not the ones actually calling the shots in most cases, considering they want people to come.
However, something as huge as EVO can completely dictate the meta... If they determine people want customs and they allow it, then every tourney follows suit as to "prepare for EVO."
God, those were awful times.
While it is semantics to discuss on Mii Specials are not Custom Moves, you can agree that they're special as you don't need to toggle Customs ON to use them.
Since these Special Moves don't pose a huge impact on the overall metagame (if any), I don't see any problem on allowing them.
Customs are inherently specials, that doesn't make them any less of customs. The loophole is just that... A loophole.
They do pose a huge impact on the overall metagame, because we're allowing characters to have customs when the rest of the cast can't. It doesn't matter if the Miis are low tier or top tier, that's not the point.
Totally gonna practice that
cough cough don't forget to watch my way past cool tutorial on it cough cough
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