Well. You can’t prerender a BGP announcement at your ISPs border. So your locally cached prerendered version on -insert some random ISP here- will always be slower than google in 99% of the cases.
Been competing against google since 2005, I’ve seen a thing or two.
For sure you're not going to be faster than google. But if you're site is > 3x slower than AMP, people will notice and prefer AMP. The point is to stay competitive.