That work made poor coaching but great training.
Idea being communicated is that the work wouldn't be considered "good coaching" but it was "good training." Note that I am not using an article before good coaching or training.
One could say "That work make a poor coaching but a great training," but this would express a different idea -- an idea of a specific instance of coaching/training not generic coaching/training.
Also, one could add a preposition or some other verb form needed for it to make it look correct, but that may again communicate a different idea than what's desired. E.g. "X led to poor coaching" or "X made up for poor coaching".
Is the original correct grammatically?