Personally, I think the Whole Final Smash system (and the Final Smashes themselves) needs to be retooled for the next game, So that it can be balanced for both Casual and competitive, because I want to see Super moves in Competitive play too. You need to make the Final Smashes feel powerful for Casuals to use it, but not too overpowered that we ban them from Competitive, so the changes I would make include
-Make Final Smashes as a whole Blockable (though some could still be Unblockable)
-Heavily reduce some of the Invincibility frames on the Final Smashes, so perhaps they could be interrupted
-Make them have a different motion than the Special Button (perhaps it's own Dedicated button)
-Give the Final Smashes faster startup as a whole (this is in addition to the ability to block them now)
-Allow some characters to have more than 1 Final Smash at a time
-Bring back Transformation Final Smashes, but perhaps make it so they can be Hit and Flinched and still KO-ed, so there's actual reason to Fight them instead of Running away
-Allow Multiple final Smashes to happen at the Same time. Perhaps if Cutscene Final Smashes hit, perhaps make the screen split-screen or something like that
and just some of the changes, along with Specific changes to the Final Smashes themselves. as of right now, Final Smashes kind of feel alienated from the rest of the Characters moves