SLS is elephant in the room - but Mars Sample Return is arguably even worse
Money for SLS is separate part of the budget, its mismanagement causes reputational damage - MSR budget is part of NASA probe budget, mismanagement there causes stall, worse performances and cancellations for AWFUL amount of other projects
MSR has indeed been a mess. I think it's pretty obvious that NASA has been trying to instill a "sunk costs" mentality in Congress, and it's not working out the way they wanted.
MSR is a fine enough concept though, I think Rocket Lab's proposal to get it done is sound and the government should take them up on the offer. If nothing else, the money to Rocket Lab for MSR development would help to make Rocket Lab a more viable SpaceX competitor, which should pay off for the US government in the long run.
MSR as NASA's JPL envisioned it was a disaster. But there was a chance that someone like Rocket Lab could actually make it work without breaking the bank.
Money for SLS is separate part of the budget, its mismanagement causes reputational damage - MSR budget is part of NASA probe budget, mismanagement there causes stall, worse performances and cancellations for AWFUL amount of other projects