[Navarr]

Looking at the source - the videos aren't set to pre-load?

And don't a lot of these sources only start loading once the page has finished rendering? AMP is supposed to be fast-to-render firstmost, right?

[x1024]

It should "be optimized for mobile". 4MB per page is anything but. If you visit 100 pages per day, you'd need a 12GB data plan.

[everfree]

That assumes that you clear your browser cache after you view every page, or that you visit 100 separate sites every day that each weigh 4MB.

[x1024]

Every page weighs 4+MB, because the page-specific content on the page weighs more than 4MB. There's almost 1MB of "CSS + JS + HTML", but about 4MB of video.