True it's a single framework, my point was only the size... I mean, the amount of knowledge you need is probably the same you need to work with web stack.

Also, if you need a backend even if it's written in same language, is still a different thing, much like node and web javascript. Choosing a different backend languages usually is made because of the advantages it brings (Rails for prototyping, Erlang or Elixir for stability, Java for performance and so on)