I agree. The issue is the DOM. (For contrast, I've seen highly performant 3D worlds rendered in the browser via WebGL that don't bring my computer to its knees.

I agree. The issue is the DOM. (For contrast, I've seen highly performant 3D worlds rendered in the browser via WebGL that don't bring my computer to its knees.) We've been layering on years of HTML/JS additions that aren't allowed to break backwards compatibility. (Google's Blink project is one example of an effort to try to undo some of this.)