Marsh isn't a problem. He was 2.5 fWAR in 475 ABs. He needs to be used less vs lefties of course, but that's not his fault. He's still pretty cheap, too.
Resolving the "rotation" in CF and LF would help this team a lot, and I think Marsh is at least part of the solution.
Hays, Rojas, Clemens, Wilson, etc will have to step up or be replaced. It would help if Casty were a 140 OPS monster in RF, but he's not, nor will he be in the future in all likelihood. It would also help if Justin Crawford becomes a 120 OPS high OBP CF who can play regularly, but that's something you can't count on for 2025. And Miller is one or two years away even if he's as good as we hope.
They need more production out of the OF and out of catcher. I'm interested to see how DD proceeds.