Not sure of what does webpagetest is showing evidence of. It could be anything... for one thing, AMP versions are much leaner so naturally they will load fast -

Not sure of what does webpagetest is showing evidence of. It could be anything... for one thing, AMP versions are much leaner so naturally they will load fast - even with no dedicated CDN at all. Cloudflare and Fastly should be more than sufficient CDNs? Admittedly, maybe the AMP CDN is an easier one to set up for the masses, but other than that I bet they all have about the same performance.