For reference, we haven't spent any time trying to optimize the react website for perf. Also that front page really needs to be rethought, we haven't updated it since launch...
I updated my README file to compare page load speed with the Jekyll homepage too since it's a closer analog. But comparing to a random page that wasn't too optimized was sort of the point - most of the time, speed isn't the priority and that can make a big real-world difference for mobile users.
That's probably true of every slow site on the web. Part of the purpose of AMP is that it forces your site to be fast. Of course you can optimize a regular HTML page and make it faster, but you can't pass AMP validation with a slow site.