To me the most important aspect of Erlang is the runtime's scheduler, which is preemptive instead of cooperative. This allows the message passing, sequential code and lightweight processes to be much more effective than in any other general language or framework using cooperative scheduling (like async runtimes or coroutines in Rust, .Net, Kotlin, Lua).

You can write actually synchronous code in Erlang and the runtime makes it so that no process blocks any other process by preempting them on a schedule.