IME Kotlin is the worst of both worlds. It's like they took every cool one-liner example from Scala and said "see, you don't need a whole functional language to do that, we can just add this piece of syntax sugar and you can do the same thing while keeping that Java feel", but once you've done that a half-dozen times you end up with a language that's actually even more complicated since it doesn't have the underlying consistent core that Scala does.

I like Scala a lot more than I feel like I should. It’s weird to say that it’s a language that feels too academic while also being heavily used by enterprises. I used it a lot while working at BigCo and there were a lot of times that the language got in the way of getting things done due to the design. But it is really elegant once you understand it. It’s no Lisp, of course, but it feels somehow both pragmatic and academic in getting things done. And for writing Spark, it’s quite expressive.