Replying here, cos I promised the OP I wouldn’t post anymore in their thread about pandaren priests.
Whilst I definitely understand your logic, as far as I’m aware, every priest class that has priest available does in fact use Light (even if they don’t directly worship it), including the more obscure ones like trolls (who seem to either fall into Loa priests or witch doctors). EDIT: Obvious exception being night elves, can’t believe I forgot that pretty big one.
In terms of pandaren, however, the only priests we have seen them have in-game have revered The Light, unless someone more knowledgeable than me has examples of pandaren priests who operate under something different. Whilst The Order of The Red Crane has priest NPCs in its rank, it’s hard to decipher if these are priests in the traditional sense because of the fact none of them are named or have any dialogue, meaning they could be priests in the literal sense of being devotees of a deity. We don’t actually see them use any spells, unlike the Omnic priests of the Shado-Pan who revere The Light and use Holy spells.