> For single a web api server Elixir is going to be far behind, performance wise, against nodejs, the JVM and Go.

To some Go web api frameworks perhaps.

To the JVM, not really. The frameworks I used with it in the past (spring/play/coupleOtherSmallOnes) are throttled to the number of threads for concurrent connections. The BEAM (Erlang/Elixir) has no such limitation and it blew away my old Java servers handily just due to its concurrency alone.

And not to nodejs at all. Running a single BEAM vs a single node there is no comparison, the BEAM runs circles around it. With nodejs you can shard it out to multiple running instances to get concurrency better but you run into OS limits far before the workload that the BEAM can handle.