I think you did kind of just prove his point though. 2007 was just about the time that Haskell started seeing its big boom in popularity and the unending series of 'how to monad' articles starting popping up, so when this was written Haskell wasn't really a proven language. In other words, WhatsApp kind of DID bet their $100,000,000 on their pet language, and came out ahead as a result.

My takeaway from the article wasn't that less popular languages are bad, it's that you should definitely consider everything before using them for a really important project. If your decision is that it will be a good solution, great! As long as you understand the limitations that you will run into.

These days I'd say that Rust is where Haskell was in 2007 (ignoring that Haskell came about in the late eighties). Its gone through a really long incubation period, and is about to get released into the wild, and is getting lots of press in the blogosphere. Now is the point where people will have to decide if its worth banking everything on writing a new, real project in Rust, because right now its still not much more than the pet language of some very vocal bloggers.