But React hasn't broken userspace, at least not in regards to hooks and class components. It is still possible to develop a React app today, from scratch, using only class components. Similarly, just because Deno exists does not mean that Node has stopped existing, or even being developed. As far as I can tell, "userspace" is as safe as ever.

Fwiw, I'm very glad that Linus himself hasn't taken your attitude to new technology, and is quite happy exploring experimental ideas, such as the new Rust-in-Linux work that's going on right now.