The problem with a lot of

theory is it doesn't take her glass canon aspects into account. She can dominate characters by cutting off their options like Brawl top tiers and it's easy to say she's fantastic based on that. So why isn't Rosa (and ZSS) scoring higher? She has real issues holding her back, by back I mean top 6-9 she's still really good. If the opponent can outplay Rosa a little and get rid of Luma they can flip the tables. Rosa has a great U/Dair, crouch, luma jab, etc when she's in control. But her feather weight, tall frame that flops around when recovering, lack of combo breaker aerials and greatly nerfed everything without Luma makes her extremely vulnerable to grab combos and other characters' advantage whatevers. Without Luma, who can't act while she's in hitstun, Rosa's fastest aerial is frame 8 Uair. With Luma it's frame 3. It's like Rosa has 2 different states of play. I think this inflates her theoretical MUs; based on perfect play she could be top 3 but people mess up and get grabbed. Luma gets launched. This is why Rosa isn't as solid as Sheik or even Fox; Rosa has a much weaker other half.
- I feel like when you say "Glass Cannon" you're thinking of mewtwo. A key difference between Rosa and Mewtwo is that Mewtwo, in addition to being huge and light, isn't a floaty, so kill confirms are truer for a lot longer on him than Rosa. For an example, the Ding Dong works on Mewtwo for roughly 22%, but only 9% on Rosa. because of this, she actually lives fairly long once she's out of combo percent
- Rosa isn't higher in results because she's an unpopular, "boring", character, like Jigglypuff in Melee. Despite that, she's still tied with ZSS, one of the most popular characters at all levels. She's also really hard, which is why you don't see new Rosa mains breaking out all that often like how you'd see new Cloud or Bayo mains.
- Rosa's best comparison is probably as a lower risk, lower reward version of the Ice Climbers. People used to say the same thing about the Climbers, but they could delete your stock off of one opening. Rosa can't do that, but Luma comes back, and what's to stop Rosa from not engaging during that time? Additionally, as Kirihara
- As I said before, most grab combos have really small windows on her, because she's a floaty. If Luma's still in play, Luma also forces the thrower into shield unless they want to be hit by her after throwing.
- Luma can act while Rosa's in hitstun, actually, because Luma is basically stunned while Rosa's in hitstun, but only for 80% of the time that Rosa's in hitstun. So not right away, but she can act earlier. The only time Luma can't act is during that first part of hitstun, while Rosa's in a throw animation, while they're using Launch Star, or while Rosa's in a star/screen KO animation.
- Nair isn't a great combo breaker, but it's only a frame later than up air and flips her hurtbox, potentially moving her out of the way. Her hurtbox is also deceptively thin, she's basically a stick figure.
- Your whole "People assume perfect play for Rosa when in reality Luma gets launched" I don't get. It's like you assume that Rosa's completely helpless without Luma. Sure, she's worse, but she's not bad and is certainly capable of fighting off opponents for 13 seconds by herself, or just running away for 13 seconds.
- Rosa may have one weaker half than Sheik or Fox, but she also has one far stronger half. I feel like you really only look at negatives for a lot of characters in the game, rather than positives, in a game where, clearly, positives are more important (

being prime examples).
Rosa's matchup spread is also much better than Fox's, being able to dominate a large portion of the cast with less losing matchups. There's only two Matchups that Rosa's agreed to lose, and the Meta Knight matchup is improving for Rosa. Sheik has a better matchup spread in terms of losing matchups, but is more sucseptible(sp?) to falling victim to the game's mechanics.
I agree with you on Ness being underrated, but not to the extent of his score being above Luigi, Corrin and Marcina.