Being someone who has used one ui, fun touch os, HyperOs, Color os n Oxygen Os. I can say this in full confidence that all the statements you made here are very true and realistic.
We as nothing users should definitely recommend different types of things for the betterment of Os but we should also realise that change does not come easily n there r many factors to cover while adding a new feature.
For example nothing plays on a model of stock android but if it starts integrating more of its own applications in the ui, I am sure many ppl will have problems with it.
And having tried various Ui’s I can say that no Ui is perfect n no ui fully imperfect for everyone