I don't disagree with anything you've just said. I think I'm just focusing on the present and future, while you are talking about how we got here.
I find it much easier these days to get people to consider trying a non-Windows environment but it never goes well because of these small issues.
Of course people expect things to behave in certain ways because Microsoft had an anti-competitive monopoly and most people learned about computing using their platform.
It's an unfair, shitty situation.
But the point remains that desktop GNU/Linux has a lot of these little UX bugs, and we're not even paying attention to them. The experience isn't as smooth as Windows because we don't have dedicated UI/UX designers thinking over these issues and trying to come up with cohesive solutions.
When's the last time a new consumer-facing UX paradigm that 'just worked' came out of the open-source world? Apple churns them out, oftentimes created from scratch, and it extends to their physical hardware design (ie the ipod scroll wheel was amazing for its time, airpods are a joy to use).
The open source world makes amazing things but the UX quality _is_ a major issue in the uptake of new users today.