You seem to be taking it as given that the size of stuff should match between different displays, but you don't give any reason why that's desirable. I understand the argument for 1:1 WYSIWYG in DTP, but not for UI. I haven't been doing much DTP in the last decade.

Some people prefer larger UI and some prefer smaller — partly due to differences in vision and partly just preference — and today's industry lets them choose. Your proposal takes away that choice and thus is guaranteed to anger people.