Earlier quoted context omitted.
So what do you want? "Highest common denominator" doesn't make much sense in this context - it's functionally equivalent to lowest common denominator. You want N different implementations, 1 per platform? You think the cross-platform toolkits could be better? Do you have an explanation for why they are not?
Look at WebGPU. Still a WIP, but it shows that you really CAN provide a performant cross-platform... platform if you're really thoughtful about performance
If you're suggesting WebGPU, you're really suggesting a drawing technology, not a GUI toolkit.