See, when you're talking about rendering, you're saying millions. And even then you're talking about millions of elements in a physical simulation, all interacting with each other etc.

The browser struggles to display even a few hundred elements. You can't even animate something efficiently if that touches even the smallest part of a layout.

So yes. There's a difference between the two. The browser at the core is a system for rendering a page of text and a few images. It's unbelievably inefficient for almost literally everything else.