Delays are par for the course when it comes to rocket engineering, especially new designs. There's a reason why some companies/agencies still use tried and true spacecraft models designed decades ago.
Having said that, SLS is so delayed and riddled with issues it deserves its ridicule. Starship hoppers began testing like, what, two years ago? If they have a functioning 1.0 model next year that's a very fast pace for that they're aiming for. I don't know how heavily NASA engineering factors into SpaceX's success, but the company itself has to be doing something exceptionally well when they're this fast compared to SLS and commercial competitors like Blue Origin.
I do expect Starship to blow up a few times before they nail a steady success rate. It was like that for payload-ready Falcon 9.