SLS also had a lot of welding problems that needed solved, the main difference is the engineers spent lots of time doing it on paper.

Here’s a fine article about the changes to the friction stir welding system they were using on the main tanks: https://www.nasaspaceflight.com/2017/05/sls-core-stage-recovering-weld-pin-change/

I can absolutely see that iterating with physical hardware can be a lot faster, but it can be costly if you have to build custom welding rigs for each new iteration. Starship can iterate like this because it’s still a bunch of dudes welding it by hand.

I’m presuming that over time they would introduce custom build rigs and machines to replace hands on labor and remove human inconsistencies.
The Circumferential welds in the middle are the logical place to start, but none of those have failed so far.