The Erlang thing is different though - that's a userspace scheduler, scheduling userspace tasks onto one-thread-per-core. Classic M:N scheduling in a similar way to go.

It works extremely well at scale - you can handle 10k connections on a normal machine with very little thought, and WhatsApp has reported handling 1 million. Yes everything has some point at which it won't scale, and apparently that approach (or at least that implementation) struggles at 100 cores. That's not a normal machine.