Sorry to jump in after the game, but I’d really like to respond to this point.
Personally (but this is just my opinion), I find it quite unpleasant to have to create several files (such as dune-project) in order to start getting a simple executable. I often find myself going back to ocamlfind and ocamlbuild in certain situations to quickly iterate through my work (which, in my opinion, is a failure of dune as it cannot handle such a use case).
I even sometimes regret certain possibilities offered by ocamlbuild (notably the ability to produce your own rules in great detail).
Finally, I never understood why we lost the {build} tag for dune in the description of opam dependencies. Again, from a release perspective, I think this was a big mistake.
That’s my two cents based on my experience. These points always make me reconsider dune as the solution. So I continue to try (much to the misfortune of some) other possibilities for building my software.