To note, I think GP on Ness is really silly and that should be fixed.
The cause for considering Rosalina broken is because she functions well even without Luma, and unlike Nana, Luma respawns on its own. Nana never comes back,and Popo doesn't function very well without her. But it should definitely be noted that the Ice Climbers had much better strength together than Rosalina and Luma do.
I don't find that suitable enough to warrant the label of broken. In terms of Competitive factor, it'd be SoPo < SoRo < Rosaluma <<< IC. Rosalina functions decently without Luma, but she loses a lot of control of the stage and has to resort to a very defensive playstyle. Her moveset is designed as such, which is why F-air and N-air covers so much range. As stated before, she's still juggle fodder if you manage to get her in the air, and GP is not nearly as difficult to handle as perceived.
While I grant that Luma respawning is a big point for Rosalina, that's the only point she has. Nana doesn't respawn, but she also doesn't have a limited amount of HP, is capable of grabbing, has far better control, and needs to be KO'd/gimped off the stage like Popo. The Ice Climbers have literally done everything Rosaluma has, except better and is capable of doing more, and are capable of doing a 0-to-death on the entire cast. Nana doesn't need a respawn timer because her presence is an extreme boost to Popo's arsenal, and a good IC player will keep Nana alive for the majority of the match.
The reason why I bring this up is because the evidence against Rosalina is, quite frankly, anecdotal. Rosalina is a strong character, but the metagame hasn't developed and character assessments are rocky at best. For instance, the Mario boards are still experimenting with custom movesets and combos from d-throw, and match-up discussions have barely taken place, anywhere. I just don't see why everyone is screaming bloody murder when this game has barely got off the ground as is.
