There aren’t that many books in OCaml unfortunately 
RWO is on my book shelf for now, as I’m going through “OCaml from the very beginning” first.
I’m glad I bought it! It’s a wonderful, wonderful book, so well put together.
Since I’m French, I also bought the book “programmer-avec-ocaml”, which I was very disappointed with. I stopped very early after rendering the Mandelbrot set section so I intend to get back to it at some point. But anyway, I couldn’t imagine any non-french speaking individual getting anything out of it.
From what I can gather, Core has introduced breaking changes to “make things better”, such as pushing the programmer into not raising exceptions, etc. so if this is the case, it looks like a good call to me and I’ll gladly read that book and see what techniques it recommends.
To me, this sounds a lot like the arguments in the Haskell community where no one can agree on how to make the standard library evolve because of breaking changes so it stays with its cruft, which is “subpar” by today’s standards.