You say this as if the GUI is a major part of a browser's compute budget, and not wildly smaller than rendering the page you asked for, in >95% of the window's

You say this as if the GUI is a major part of a browser's compute budget, and not wildly smaller than rendering the page you asked for, in >95% of the window's available space. I wouldn't care one bit if the GUI was rendered in immediate-mode software rendering, if it worked. I interact with websites far more.