Of course... if you don't mind a completely different language and runtime stack... there's always Erlang & Elixir!

This is true, but they come with a different set of tradeoffs w.r.t ecosystem, tooling and performance (which turns into per-node efficiency in this case). There is also a matter of comfort and team/personal preferences.

What do you mean by per-node efficiency?

Amount of work a node can perform in a distributed system per X amount of hardware resources that it has.