Rather than AB or PA I would go with something that included number of RBI possibilities somehow. Of course that starts with one opportunity every AB. I think that would take care of a situation where one hitter had a much larger number of base runners when he hits.
I agree that would be the most precise measurement. In fact it’s one I do as part of the regular stat package. Please see attachment.
Unfortunately, although the information is becoming more widely available, right now it isn’t something available to everyone.