Page Speed Insight mainly measure how fast your above-the-fold content loads. It doesn't matter if your page loads a bunch of heavy js and images as long as it's deferred/lazy-loaded and doesn't block initial render. For example, amp pages actually load a lot of js for its component, but it doesn't block above-the-fold render and thus scored really great on page speed insight. Personally, I think page speed insight is one of google's strategy to encourage people to use AMP more.
Edit: Also, I find it comical that when you include recaptcha v3 on your website, your page speed insight score can drop almost 20 points. It is as if google don't want you to use recaptcha at all.
> but it doesn't block above-the-fold render and thus scored really great on page speed insight
Which is ridiculous and just builds in the ability to game the system, because in my experience, amp pages take upwards of 5-8 seconds before anything of use to me actually loads, while the non-amp version loads in a fraction of that time.
I imagine someone is benefiting from amp, otherwise it wouldn't be used, but I have not experienced a single case where the amp version of a site wasn't significantly slower.
Last time I tried WebAssembly website that's loading 4-5 MB of data and it managed to score something like >95 meanwhile page was ready after like 5-10sec.
Edit: Also, I find it comical that when you include recaptcha v3 on your website, your page speed insight score can drop almost 20 points. It is as if google don't want you to use recaptcha at all.