alt Hacker NewsSites can be fast with PHP and JavaScript. The slowness you see is mostly coming from all the frameworks too many developers "include" willy nilly with code that can only be described as bloat because 99% of it is completely unused, yet being loaded and computed by the browser on every load. That's what you're experiencing on too many websites.
Funnily enough, since most JS frameworks are utter junk, developers are better off instructing LLMs to write pure JS instead.
Fun story, I was writing some 3D graphics animations for a website, and the only dependency I allowed was three.js. It ran well, but the site was loading slightly too slow so I told the LLM to optimize. It essentially hit a hard wall and told me something along the lines of "I can't optimize further, three.js is the bottleneck due to blablabla, but you don't need it. If you want I can rewrite it with pure WebGL". I said sure and load times were cut by like 90% and framerate went up too. Staggering.