You made the claim that they stil speak Orcish. The fact that not one single Lightbound orc continuing to speak orcish. Additionally, Auichodon houses draenei spirits. Not orcish ancestral spirits or elementals. There’s no evidence supporting your claim that the Lightbound are preserving Mag’har language or religious traditions.
The the Iron Horde was defeated by Draenei and other Mag’har over 30 years ago and the generation of orcs now is pretty much too young to have even joined. The High Exarch’s sermon plainly states they’re doing this to create an army united in the Light that they believe will bring order to countless troubled worlds.
Lightbound are the violent aggressors in their conflict with the Mag’har. Them referring to Mag’har as “savages” clearly isn’t a reference to use of violence.
Yes, what the Mogu did was also genocide. There have been multiple instances of genocide in the history of the Warcraft universe. The Lightbound do not fall short of the term. That any orcs exist that aren’t either dead or converted to the Lightbound is simply because the Lightbound hadn’t gotten them yet. We see Lightbound continuing to try to kill and convert Mag’har. They’re still in the process of committing genocide.