This is not a good explanation. AMP4Email is different from AMP and serves a different purpose. https://medium.com/@pbakaus/why-amp-caches-exist-cd7938da245... is an explanation of what AMP does.
It is not just Google (and Microsoft and the other companies that implement AMP caches) that believes users want instant loading. Apple and Facebook have products competing with AMP that give users instant loading but that are far more restrictive on the publisher and on the reader. The only reason that publishers and readers put up with that is instant loading.