Our modern political and legal definitions of genocide don't necessarily mean total extermination, destruction of culture can also be a form it takes. I don't think you could reasonably say that the systematic intent was present and no-one would have attempted it outside the direst of circumstances, but in another context I'd be comfortable calling the destruction of Vulcan in the alternate reality an attempted genocide because Vulcan had colonies but their homeworld was central and a majority of the species died and their entire cultural history was eradicated, not to mention anything in their biosphere that wasn't exported was rendered extinct.

Klingons had enough colonies to have epidemics during the Enterprise era, but I don't think we've seen any planet given anywhere near the same importance. As we saw from the mirror universe, if Starfleet used that bomb, it would result in the destruction of the majority of klingon culture with the remainder as struggling refugees and freedom fighters. It'd be more like deploying a weapon that destroyed all the Japanese islands and then claiming they survived because their are still pockets of expatriates around the world.