SLS is a solution for the problem of the US needing a large launch vehicle. That's not the issue. The issue is that it's taken way more time and money than anticipated and hasn't shown good results.

Budget and schedule overruns are expected with any large project - it's just the nature of contracting. But there are limits, and SLS blew past them quite a while ago. I'm not sure how much of it is NASA's fault given how much congressional meddling has gone on, though.