But is it on-par with native offerings? Where are the standardized components? How many years did it take to get a simple grid layout present in Tk back in 1991? Where's the fool-proof GUI editor? How long did it take for it to have a date input?
The web had to fight its way to where it is now. And that's why it has so many scars (besides the self-inflicted DOM and Javascript before strict mode and ECMAScript 5).
Regarding the OS vendors, well, yes, kernels, tools, basic apps. Also not all applications are graphical.
Before web stack there was Flash it had hardware access but it was insecure, now web tech going the same way with web assembly and webgl.
They're supposed to. They're fitting in with the OS's native look and feel. And that's a GOOD THING.
So it is definitely possible to make a framework/toolkit although if you look at development history of browsers how many years it took them to get where they are and Opera throwing in the towel and switching to Blink.
Only question is, if they do such a toolkit what is there remaining for OS vendors to do? Kernels? Users will just choose faster one.