You probably don't like what I have to say, but; I've come to realise that human beings are far from uniformity or consistency, and the computers we produce are a reflection of that. Expecting, or even thinking that you could have total consistency and for everybody to follow one standard is a rather autistic view that often doesn't align with reality.
Something we perhaps should have done, is build a webkit-like engine that would have been highly performant. Something implemented as a low-level library that all programs could use, and would provide layout, shape and text primatives without the full bloat of a WebKit engine.
Reason being; using webpages was always too attractive of an option for GUIs. 1) HTML is much simpler than Win32/Qt for creating a layout and populating it, 2) People will always abuse GUI toolkits. Think about every Win32 form with 36pt font buttons or pink text on a white background.
It would probably be better to let people resort to creating their own GUIs from the get-go, without resorting to garbage like Electron, and terrible markup langs like HTML/CSS. You lose a lot of UX with non-standard interfaces, but you kind of get that already with shit performance, so I'd say it's lose-lose already