Thanks for the clarification, that makes sense.

It is ironic that the vast majority of these performance issues are caused by render-blocking and CPU-sucking JavaScript, and so the recommended approach is to install yet another client side JS library (https://github.com/GoogleChrome/web-vitals/), which appears to only work in Chrome, and then use the library to post client side performance data to Google Analytics (though to be fair it could be any analytics).

"How badly are all your JS libraries slowing down your page? Find out with this one weird JS library!"

This seems like one of those things where if you get to the point where you need this, you're already in too deep.