It takes more than just a large sword to beat Rosa.
Just emphasising this point, which people seem to forget, or just assume that sword = good Rosa MU.
Yes, swords can make dispatching Luma safely a little easier, but they are still attacks that will leave you open, and a good Rosalina will punish you for that. In most cases, sword characters frame data is a lot stricter anyway (be it active frames shorter, autocancels stricter, startup slower etc). In addition to this, pretty much all sword characters don't land easy anyways, which just make's Rosalina's arguable biggest strength stronger.
Plus, when Rosalina is without Luma, she can simply run away, and most sword characters don't want to be doing heavy approaching, as it is often committal and easily punished. My favourite thing to do is simply F/Bthrow and then run away (it's an arse way to play and it annoys folk, but it works).
Like, Marth and Lucina do decently well in this MU compared to the majority of the cast, simply because they can deal with Luma safer than others. However, Rosalina has more than enough to bat back their way. Them having next to no ways to land against her safely arguably evens the MU out. This is probably an even MU at best. I could personally see this MU anywhere from 50:50 to 55:45 Rosalina tbh.
Ike definitely doesn't do that well against Rosalina, mainly for all the reasons I explained above about Marth/Lucina, but worse. Most of his moves can swat away Luma fairly easy, but they're unsafe, he can't approach Rosalina safely if she runs away, and he just gets juggled even worse (also, Star Bits can be kinda silly at stopping Ike's recovery if he doesn't space it correctly).
Though his Bair is legitimately a great move in this MU. Doesn't even out the MU but it's definitely his best tool and a move Rosalina must respect.