I agree that many FSF/GNU projects have made horrible technical choices, but I don’t think that’s really the root cause here. The reality is that good software requires an enormous amount of skilled labor to create and maintain, and the FSF and other OSS orgs can only muster a small fraction of the engineering hours that a mid-sized for-profit software company could.
In addition, good user-facing software requires more than just good engineering - you need good UX, product direction, etc. Sometimes the creator or maintainer of an OSS program will have the good fortune to be reasonably good at all of these, but it’s very rare, and there aren’t nearly as many UX designers or product managers looking to contribute to open source as there are developers. Even if someone did want to help in this role, the developers on most projects would probably ignore them.