Concurrency != parallelism. You can of course run a multi-process cluster, but that’s besides the point (and these days it’s best to run a single process inside orchestration like k8s).

Basically almost every high performing server atm is running on some form of event loop / cooperative multi-tasking. Ruby Puma, Gunicorn, rust’s tokio and async/await, goroutines... Java is probably the big exception here (if you’re not using VertX et al) and we all know the pain of thread safety.