Edit: Also how hot is my phone?
Edit: Also how hot is my phone?
It's so convoluted, and very app specific. Core web vitals provide the right framework to think about what is relevant, but in reality your app likely requires dedicated instrumentation to capture these phases accurately.
React etc. runs just fine on absolute garbage kiosks. If you introduce 10MB of additional JS on top of 60KB of React, it's those 10MB's fault.
Hate me if you will, but holy fuck. "Downloading this code takes WAY more time than running it" with NO parameters whatsoever on what the code is doing is an absolutely ridiculous assertion.
Most React apps don't put an infinite loop in their components. The vast majority of the time it sets up initial state, maybe sets up a skeleton while loading some customer data, then shows a page with a few sections and a dozen inputs.
So "holy fuck" you should probably calm yourself down.