May I ask why Miyabi and Hidden Garden are banned stages? I understand the Pirate Ship, Training Stage and Unforgettable aren't tournament viable stages but those 2 I'm not too sure about. Are there bugs in those 2 stages?
It's safe to consider that the stages are banned due to unfound bugs. I am not given the reasons for the ban, but the World Championship ruleset is the current suggested ruleset as it's the lead tournament circuit for the time being. Personally, I'd have no stages banned besides the bottom of a finite stage.