Calling failed builds "damage" is rather overstating it. If building a specific package fails, OPAM continues with as many other packages as it can. Arguably that's not even "transactional" in the atomic sense, but the behavior is pretty much what you said.

Then it gives you the error, and gives you a command to roll back everything to the previous state -- something I cannot do with eg, apt, as far as I know. But that's a bit apples and oranges -- apt, yum, pacman, etc are all binary package managers, with a different set of tradeoffs.