1) There are trade offs, sometimes you trade development time for execution time.
2) Erlang is "fast"/scales, ask whatsapp
3) A lot of people worry about execution but have enough spare CPU cycles to compute the universe.
4) Benchmarks mean nothing, you must figure out what is meaningful to you. You won't compare a ferrari and a minivan? Well, you could, but yet, find that a minivan is more practical for your daily needs.
But whatsapp is not a latency-critical application.
For most other things, Erlang is a fine choice. In your other comments you talking about web pages. People compose those all the time with languages like PHP and Ruby, and things mostly work out.
Odds are, with a lot of web stuff, a decent portion of your latency is going to be in the data layer anyway.
I think WhatsApp is latency critical, no user ever said it's okay to have their message show up minutes after it was sent if both parties were on a good internet connection...