I appreciate the sentiment, but I'm not a UX designer or expert. And the problem is not that Linux doesn't have enough UI developers, it's that many of them are working on re-inventing the wheel in different, competing ways. Linux needs a dictatorial BDFL for UI - a Linus Torvalds for the desktop - an idea somewhat antithetical to the distributed nature of open source development.
It doesn't help that organizations that could be leading the charge keep changing direction. Ubuntu went Gnome -> Unity -> Gnome in the span of 15 years or so. And now they're going in hard on Snaps, which introduces breaks in UI uniformity again (Gnome Themes, for example[1]).
[1] https://www.omgubuntu.co.uk/2020/10/automatic-theme-installa...