Yeah, this makes sense.If they used him, for example, as part of a "crusade" against the undead on Azeroth that would be one thing. But that would mean a showdown with Sylvanas. So now that Sylvanas has now gone super Saiyan and opened a gateway to the realm of the dead, that can't happen and the lore of death has been sullied. Keeping in mind the original lore of the "light" on Azeroth were as forces of good against the forces of evil as symbolized by the undead scourge.
By cheapening the lore I meant the "light" itself isn't evil or grey. It is a force of the universe and should be consistent with that.
Same thing with death. But we have now introduced with "Shadow"Lands, the idea that these concepts and forces aren't as fixed as we thought and have "shades of grey".