Becoming professional, and gaining experience has given insight in helping to choose stack in respect to matureness, stability, tool support, documentation etc. It's not that you cannot write Scala code for production and be happy about it. But I rather not. Writing fast is only one part of it. IntelliJ supports the whole aspect of development cycle, and it's good to hear Scala plugin is catching up. Just my opinion.
Interesting choice of languages. Out of that list, only Haskell is suitable for the argument you're trying to make.
Is that SML or Ocaml? If that's SML, well it's a really poor choice. And what makes you think Clojure is better for functional programming? I'm not arguing that it isn't, it's just interesting seeing it in a list of what are supposed to be better choices for FP. Because in my opinion, Clojure is just as dirty as Scala or maybe even more so. And it's also a Lisp and the styles and patterns used tend to be different in Lisps, than what you do in Haskell or Scala.
That book I linked is not about Scala, but about FP and just happens to use Scala as the language. It's a good book. If you preordered it, it would be a waste to not read it.
I'm playing with Haskell as well. Cool language, the ecosystem does suck a little.
That said, it is improving and closing the gap rapidly.
> one of the biggest is IntelliJ's capability as Java IDE
That's a pretty shallow reason if you ask me, because the speed of writing code is not the point and IntelliJ IDEA 13 is also very, very good for Scala development.
> I just dislike Scala's monstrosity. I have high hopes for Kotlin
Well, there's your problem. You thought that Scala is something that it isn't, like a "better Java". If you approached it like that, without delving in its FP capabilities that Java 8, Kotlin, Ceylon, Groovy cannot match (or whatever "better Java" is the fad du jour), then of course it was a bad experience.
Next time you'll have some time to burn, start here: http://www.manning.com/bjarnason/