BEAM is not fast when it comes to CPU intensive workloads. "Better performance" has many dimensions, in many (most?) scenarios of web serving the bottleneck is latency to other services (i.e. Postgres) and not the processing of the web server, like you suspect in this case as well.
BEAM/Erlang/Elixir's main advantage IMHO is parallelism and "cheap" concurrency that's easy to wrap one's head around. It reuses multiple cores, and processes (lightweight threads) are both cheap (smaller stack size, per-process GC) and easy to get right (due to immutability of data structures and supervision). Also you'll get less spiky latency even under high load.
Node.js main advantages are the breadth of the library ecosystem, industry familiarity and its JIT compiler (if used correctly). At the cost of more setup one can also run an instance per core if they care for parallelism.
So I'd suggest that with BEAM he'd get quite a good performance both in terms of developer time and in serving many (network bound) requests on a multicore machine.
BEAM/Erlang/Elixir's main advantage IMHO is parallelism and "cheap" concurrency that's easy to wrap one's head around. It reuses multiple cores, and processes (lightweight threads) are both cheap (smaller stack size, per-process GC) and easy to get right (due to immutability of data structures and supervision). Also you'll get less spiky latency even under high load.
Node.js main advantages are the breadth of the library ecosystem, industry familiarity and its JIT compiler (if used correctly). At the cost of more setup one can also run an instance per core if they care for parallelism.
So I'd suggest that with BEAM he'd get quite a good performance both in terms of developer time and in serving many (network bound) requests on a multicore machine.