Can someone explain how an AMP page would possibly be slower?

Especially given Google's CDN and the fact it's likely to be preloaded in practice?

I find myself wondering if this isn't just some artifact of the Chrome tool being used to measure performance -- especially since that tool reports an overall score like "94", not an actual speed -- and the weightings it uses [1] could be different from what AMP is designed specifically to speed up. Also it would have to be measured across a wide variety of locations worldwide, etc., certainly if the author's webserver is in their own city, for example.

A lot more data, measured rigorously, would be needed to prove that AMP is actually slower in practice -- it's a bold claim.

[1] https://developers.google.com/web/tools/lighthouse/scoring