Rosalina had a few challenges to overcome in competitive play regarding certain other relevant MUs like Sheik, ZSS, and Meta Knight, prior to this patch. I've seen a lot of Rosalina mains cry for patches on these, and while I never really felt strongly about these other characters needing nerfs (especially not FOR Rosalina, because I thought her competitive players just couldn't handle the MUs due to Rosalina's stagnating meta, not because the character legitimately couldn't handle the MUs), the fact remains that these nerfs HAVE happened, they are mostly EXACTLY what competitive Rosalina mains have been asking for. Basically, while Rosalina didn't receive any buffs directly in the vein of Samus and Mewtwo, she quite literally might have received the biggest (indirect) buff of all, and that's an already amazing character having her main competition nerfed in areas that REALLY matter.
While I have ALWAYS thought Rosalina had the best POTENTIAL out of every character in the game and COULD take the #1 spot (which I don't think is unreasonable to say, considering the endless creative potential she has due to Luma's mechanics), she has always been #2 or #3. Some people even believe lower, thinking she's "barely viable". I've always agreed with the #2/#3 placement, because the fact is that not many people play Rosalina, and of those people that play her, they don't show up very frequently and aren't as good as Sheik players. Even Dabuz, is right behind Nairo and ZeRo in the rankings, because fundamentally, he's not as good a player as those two. Regardless of who he plays.
However, in light of Dabuz and his Rosalina play improving recently (he just won a tournament with Rosalina right before this patch, and it was filled with Sheik, ZSS, and Meta Knight, Rosalina's three big adversaries before in the eyes of most), and in light of this new patch removing a lot of the primary MU issues Rosalina had against other characters, I think more than ever, it's fair to say Rosalina is an obvious contender for the best character in the game. Also, this may not be relevant, but in the Irish competitive scene, a Rosalina player, MiNT, has been DOMINATING with her for the past few months over here, and IIRC he's been doing so well that he's dropped Sheik as a pocket main (the Power Ranking used to display both Rosalina and Sheik as his character IIRC, but now it's just Rosalina).
HOWEVER, Rosalina as a fighter has one main big hurdle left to overcome - her player base. Rosalina players are infamous for not being able fully utilise their own character. Go to the Rosalina MU boards and you'll see Rosalina players claiming all sorts of characters are bad MUs for Rosalina, to the point where one would be perfectly justified in asking "if she really has trouble against all of these characters, why is she top tier and why is she such a dominant character?".
These nerfs that recently happened to Rosalina's competitors are EXACTLY what Rosalina mains were whining for, their main issues have been "fixed", but I feel she will still struggle against these characters if her player base doesn't start innovating and using more of her tools, and doesn't quit this "exclusively hyper defensive" playstyle that has PLAGUED this character's player base since day one (hyper defense has it's place, but in some MUs, exclusively focusing on it too much is asking to lose when there are much better options Rosalina could be using. The Captain Falcon MU is a great example of this). New blood in Rosalina's player base could also really help and is more likely to happen if her competitors are to see such heavy nerfs, but even that may not happen because Rosalina is an unorthodox character, and one of the least beginner friendly and most technical in the game at high level play. There's also the fact that the Smash community just really has a bias towards obvious "super flashy and fast anime cool dude/babe swordfighter/brawler" characters. You know, like Sheik, ZSS, Meta Knight, Corrin, Marth, Fox, Captain Falcon, etc. Both from an aesthetic and meta game standpoint. Rosalina CAN be these things but she doesn't look it at a surface level. Playing rushdown Rosalina, for example, takes a lot of practice and you need to master some key techniques, such as Lunar Landing.