The only reason I bought the quest pro was for the pc I have no interest in the stand alone thing and I would think most people who bought the pro are the same.
I bought the Pro because Youtubers were raving about how good it was for PC, and I needed something clearer and sharper than my Index. The fact it can also replace my Quest 2 for standalone is a bonus.
Some developers have bought one for prototyping AR games though, as though the passthrough isn't amazing quality the actual AR experience is pretty good.