Taming undead did actually have some PvP impact, with certain CC working/not working on undead. It's why hunters who try and push the absolute limit out of their class will have both a normal raptor(Or other cunning mortal strike pet) and an undead raptor and then switch them out depending on what they're facing, to minimize the amount of possible crowd control on their pet.
Demon Hunters suddenly doing holy damage could also have a big impact, with Blinding Light from Paladins not breaking on holy damage, that'd be an extra stun to try and kill in whilst being on a completely different diminishing return. Though I don't think that necessarily disproves the leak or the possibility of damage types changing, the effects of it aren't nil.

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