That is not entirely true, there is some overlap but also enough distinct features on the language level to make a difference. For example object oriented features in OCaml are quite different, OCaml has a more powerful module system (functors), it has open polymorphic variants, extensible syntax. F# has also a number of features that Ocaml hasn't, but it is definitely not true that one is the superset of the other.

The runtime situation is arguably also a matter of preference, Ocaml compiles down to fairly efficient machine code and has a well tuned garbage collector, whereas F# at least initially had to rely on a garbage collector that was tuned for a different use case.

You give a very clear overview of the differences between the languages and I agree it is important to stress that there are significant differences between the two. The OP mentions mobile development though and if the goal is to ship apps targeting iOS and Android, it is not going to be practical to use OCaml- hence my suggestion.

For me F#'s syntax is so clean and pleasant to look at, I just love it. But having been in the JVM land for too long, at the beginning I like to get a bit more 'native' and learn OCaml. Hopefully acquired functional programming knowledge can be transferred to F#+Xamarin app development later.