[roqi]

> Rerendering and recomputing too much (ever encountered these chains of map() and filter() in render()?), many API calls, huge icon sets, huge custom fonts, CSS frameworks and JS frameworks, huge dependency trees with many instance of the same lib running sometime in several versions, big bundles...

This hits the nail in the head.

A single high-res background image weights more than all the code in a complex webapp. If that image is required to pull the first contentful paint then the page will feel slow.

It matters nothing if your JavaScript is just a hello world console log. That background image is in the critical path.