Nowadays, we come across many websites where the pages are too slow. They take a while to load simple content like thumbnails, texts, and pictures. Most of the time, these pages are slow not because of your internet speed, but because of the technology the websites use for serving content
A page could load thousands of images and thousands of tiny CSS files.
None of that is JS, all of that is loads of extra requests.
Never mind WASM. It’s a portable compiled binary that runs on the browser. Code that in c#, rust, python, whatever.
So no, JS is not the only way to poorly implement API requests.
Besides, http/2 has connection reuse. If the IP and the TLS cert authority is the same, additional API/file etc requests will happen over the established TLS connection, reducing the overhead of establishing a secure connection.
Your dislike is of badly made websites and the prevalence of the browser being a common execution framework, and is wrongly directed at JS.