It might just be me, but that sounds like a Ridley question. As in, "Why would details of a character in their own canon affect their viability in Smash Bros".
Which it doesn't. People can think it does, but it doesn't. Villager was booted from consideration in Brawl because in his canon he doesn't fight. Look how that went. Wii Fit Trainer doesn't fight in her canon either. Neither does Sheik. Neither did Peach or Zelda really at the time of Melee. And ROB is a video game peripheral, so I mean he's there for his historical significance and not even because he's from a video game. And don't even get me started on size and proportions in canon, because everyone is scaled to the same standard if they are made playable. They aren't made playable if they are already within the standard, that's not actually how it works and that's all I have to say about it.
Also, my point with Roy and Rosalina is, Roy was the star of his own game. After his appearance in Melee. If Rosalina got her own game come 2015 or so, entirely hypothetical here, then it WOULD literally be the same thing. I am not restarting this conversation, I am clarifying for past reference.