It's not as simple as total page weight - latency and server throughput are also important. AMP pages are likely served from a fast global cache with low latency from all over the world.

As mentioned by others, page weight is a bit tricky. However, Google has this thing called "Google Page Speed" and that would actually be a pretty good indication on the performance part.

Then again - any site with good performance can be made unusable by crazy marketing people who wants [insert tracking tool here] on every page or similar.

Absolutely this.