Google PageSpeed Insights is optimized for the mobile view of desktop page, and the desktop view; it does not yet have a test for /AMP/ mobile framework, which will only be loaded and cached by those platforms supporting it.
So, testing for “speed” based on PageSpeed Insights is not yet a valid metric.
AMP doesn’t work the same way your mobile/responsive version page is loaded.
You may want to go review how AMP works; it’s NOT intended to speed up your existing theme, but it’s a secondary element for a new method of loading mobile content very quickly, or “almost instantly.”
There is an entire website about it, if you Google it, or check the plugin docs ??