Also, Sonic gets invincibility frames on the way up in his recovery. So despite not being able to attack on the way up, he's well protected even on the way up. And his fast fall is very quick, while regular fall is not very fast vertical movement-wise, giving him a lot of options.
Rosalina is not protected at all on the way up/across (even Luma cannot attack on the way up/across), and is completely vulnerable if Luma is not around. On top of that, she falls quite slowly regardless of which type of falling she's in.
Rosalina's recovery serves no other purpose than to get her back on stage, to be used as an evasion/get-away tool, and to be used for off-stage mind games (this sort of groups under getting her back on stage, though). Also, you CAN use it to follow up on combos if Luma is present, but because the move is angled and such, this is harder to do than with Mega Man or Sonic, especially because Luma does not have as much range as them.