If that Erlang developer knew Elixir, and threw together a simple Phoenix web app which pulled the optional Node.js/npm dependencies, you could definitely throw

If that Erlang developer knew Elixir, and threw together a simple Phoenix web app which pulled the optional Node.js/npm dependencies, you could definitely throw together a spreadsheet in a few hours, with added uptime/reliability guarantees. That being said, your overall point certainly stands. I wouldn't write an OS in Fortran, or a game in Ruby, etc.