As a recent migrant from Ocaml to Scala (due to stagnation of Ocaml), I have to say that you are quite right about type-annotations, but the style of programming that an Ocaml/F# person would be accustomed to is quite easily replicable using Scala.
By stagnation I mostly meant the comparatively tiny ecosystem of libraries vis-a-vis, e.g. JVM-based languages. In particular, with Akka, Scala has much nicer support for concurrency. The ability to call, and be called by, Java code in the smoothes possible way is also beneficial for my use cases.
I'm surprised that GADTs were added, because a few years ago I visited the Gallium team at INRIA who develop Ocaml, and asked about GADTs. I was told by one of the senior Ocaml developers that there were no plans for the inclusion on this feature.