40K will always be held back by the fact that its defining characteristic is grimdark, and everything is ultimately subordinated to that in the long run. The Tau can never be both good and successful in the long term, since that wouldn't be grimdark enough.

It's at its best either in alternate timeline counterfactuals where the grimdark narrativium can be removed, or when it embraces the fact that it is a ridiculous piece of camp escapism that comes from the same sci-fi milieu as Red Dwarf.