Something I wanna talk about this fight...
Is it just me, or Rosalina seems to be way too hard for a "Normal Mode"? I don't know the way you balance this fights, but it does seem that you guys take in count the use of save states. Personally, I try to avoid using those 99% of the time because that feels like cheating (unless is for testing purposes). I know I'm not the best at RPGs either, but there's no way you'll be able to legitimate beat her. My only complain about this fight is that the Lumas come back way too quickly (3 turns). Not only that, but she casts a devastating attack pattern every time she loses a life, which may lead to even 2 dead party members, and that means that you'll have to waste 1 turn on healing (if you're lucky, you won't get one-shoted by Galaxy Beam). By that time, at least 1 Luma may have already be brought back because there's no guaranteed way to defeat all of them at once (unless you're lucky with RNG). And she has 15 lives? Yeah, "secret boss at Yo'ster Isle" is nothing compared to this.
In other words, to balance this fight, the Lumas need to take a bit longer to come back. 5 turns seem fine, but if you think it's too much, 4 should be enough.
That's all I think about this fight. Let me know what you think. If you agree or disagree, I'm still curious about your thoughts.