In relation to Little Mac, I think he is overrated even on FD, but he's still problematic in a way that he rewards bad play in some ways. He's fun to fight in the right hands though, good Little Mac players are a good time.
There is a friend of a friend of mine who mains Little Mac, and all three of us played together for a good while last night, mostly on FD. We did the same a while ago, on the game's first weekend, and the Little Mac player dominated. However, fast forward to last night, and me and my Rosalina actually dominated. I honestly had a little bit more trouble against his Mario.
Still a really good player though. I just think Little Mac VS Rosalina is in Rosalina's favour. However, Little Mac will thrash a noob Rosalina, since the match-up is only in Rosalina's favour because you can exploit certain things about Mac, something lesser players won't do.
However, this player didn't know about Little Mac's gimping trick. I did tell him about it though after we were done, so we'll see how things go in the future. Though it won't really effect Rosalina so much, since she can escape it...