I'm not quite sure what you're getting at there, first you make the arguement that it shouldn't have been asked at all and then you finish by saying they should say persons on board instead of souls on board, is it the terminology or the fact that it was used during an emergency that you're objecting to?
Also, I thought ATC could get the amount of seats sold for a particular flight off the ops department anyway, wouldn't that give them a max number of people that would be on board anyway?