I think the issue is that the SNP have had to prove devolution doesn't work to advance their case for independence (wesminster doesn't let us do anything, big rotters that they are, we need more powers).
I think Labour need to/will actually make devolution work once they get in. And having got in, I think they have the best chance of doing so - Scotland is now no longer the branch office as was the case with Blair/Brown/Lamont etc but instead is now the tipping point that Starmer knows he needs to keep sweet to keep himself in no.10.
ETA - and if Sarwar can prove himself to be a clever cookie, he has the real potential to hold the kingmaker role and balance of power in the new Labour Government.