The Lumas did not sacrifice themselves to recreate everything. People misinterpret what Rosalina meant by that quote:
-She says Lumas CAN be reborn as planets and galaxies, but she never says it's the only method of their creation (which we know for a fact they aren't, as there are a couple of occasions in the Galaxy games where you make planets appear out of thin air after doing a puzzle).
-Even if you assume Lumas are the only method of their creation, someone still needs to create the dimensional space for the planets and galaxies to reside in. That was clearly Rosalina, as you could see her light emanating from the center of the universe, not to mention her being in that giantess form in the ending, as she spoke to Mario. Her and Mario (likely as the result of Rosalina protecting him) are the only two characters we see definitively survived the recreation of the universe without being consumed by the black hole. We visibly see Peach get sucked in, meaning she most likely disappeared from existence (meaning Rosalina simply brought her back or reformed the atoms that make up her body - a theme that's already addressed across the game), but Rosalina creates that big burst of light (which is most likely a big bang) before Mario is sucked in, which is how he survives. And also, you cannot argue that Lumas can create dimensional space. It's never shown that they can, and Rosalina never mentions it. On the other hand, Rosalina literally has a universe up her gown in Smash. That's dimensional space and planets within it, by definition. Some people may argue that "Smash isn't canon", but for well established characters like Rosalina, they at least adhere to the powers and roles they have in their original games. So while she isn't shown to have this in the Mario games (because we rarely see up her gown in Mario games, never intentionally anyway), she WAS shown to have the power to create universes. It's not a stretch to believe she can have one inside her gown at that point.
-A lot of people point to Young Master Luma waving goodbye to Mario and falling into the black hole as the evidence of Lumas sacrificing themselves in the ending. That would be fine, except YOUNG MASTER LUMA NEVER TURNED INTO A PLANET OR A GALAXY. He's in the secret ending, clearly still a Luma, and he ends up getting left behind on the Gateway Planet after Rosalina takes off. He then jumps up and teleports somewhere, and then in the opening of Galaxy 2, Mario finds him once again, though he has lost his memory (presumably because he fell to the Mushroom Kingdom somewhere along the way). Fast forward to the ending of Galaxy 2 where Rosalina and Young Master Luma are reunited, where Rosalina says "after that monster stole my Power Stars (referring to the events of Galaxy 1 - as Bowser never stole anything from Rosalina in Galaxy 2, as the Comet Observatory is clearly up and running in full functionality, and the Power Stars you collect in Galaxy 2 fuel Starship Mario), I was separated from my little one (referring to the secret ending of Galaxy)". This means it's impossible for Young Master Luma to have sacrificed himself to turn into a planet or galaxy, meaning the ONE PIECE OF VISUAL EVIDENCE THAT PEOPLE CITE as Lumas being the only thing that creates new galaxies, is not evidence of it at all.