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...