Rosalina will only thrive more in stages with platforms, as both Rosalina and Luma have plenty of attacks that go right through platforms, and they are hard hitting attacks. And technically, all of Lumas attacks will easily go through if you position him in such a way.
I don't think Rosalina is under the Dedede effect at all.
The Rosalina meta will never stop evolving, as she objectively has more possibilities than any other character, and just has too much she can possibly do. She's not bound to being rushdown, campy, or anything. It's really up to the player. While most other characters are stuck with a specific style of play they excel at.
Rosalina is the one character I think will show off the raw skill of each individual player.
EDIT: Also this seems relevant: