I have used SML, OCaml, Haskell, and many other languages, and I like Go, and use it for almost anything I do these days. So your statement is false. The only thing I did like more in functional languages was writing compilers (which ironically happens to be what I'm doing now in Go).
I didn't carry out a scientific study -- to my knowledge, no one is bringing any hard facts to the table when they talk about programming language preferences -- so you can't evaluate what I said as logically true or false.
For reference, I have used OCaml, Haskell, Golang and C extensively. I think Golang is a wasted opportunity to replace C. It's a mediocre language with a bunch of annoyances.
Indeed, ML was more advanced at the time of release, and has been improved since. However I won't blame C, since C was much more successful and (as Javascript knows well) it's very much harder to make changes to a language when you have to maintain backwards compatibility with a vast body of code used in production.