im not sure how things where before, but right now im at a points with my priest (level 91) that its not worth for me to due and stick together with some1 because he gets the exp for doing more dmg.. only way i get decent exp is by splitng from the party member and get kills myself.
some numbers for exemple:
when i due with a level 86 white knight in blue & black kents when i split from him and kill black kents and he kills blue i get 1.6m exp ph (and the map has ok spawn nothing more)
when i due with him on blue kents map and we stick together i get less then half the exp (about 700k ph and the spawn is much better in this map we are clearly killing more mobs per min)
same gose for DK due in deep ludi\himes - its better for me to get HB mule and solo\due with low level priest
so i would say that priest get penetlized for half the potential EXP they could have gotten for not doing the dmg (but they support the DPS who dose)
if i would have gotten heal exp that would somehow make up for that exp gap so that would be fine, then both sides benefits, and priests can actually support their party insted of giving HS and split.