What you say about in terms of comparing download size: This very much depends on the site. It might be that you're right in terms of trends. I haven't seen an

What you say about in terms of comparing download size: This very much depends on the site. It might be that you're right in terms of trends. I haven't seen any statistical evidence, but from my personal experience a typical website with some images, some JS is often heavier on the image side. Fonts can be large too. PNG are heavy. Videos are the heaviest but rare. However per byte impact on performance (which is a very vague quality) is very different. Often JS degrades performance more than images.