Not sure how well that idea would work to be honest. I have a fair few low-sed friends and i tend to help them out now and then. If i got nothing from it, i think i'd be less inclined to actually help them. That said, you do get less EP for lower level enemies, so i doubt that is really an issue. The really good EP lies in taking down the higher bosses on your own where you spend a lot of focus and get both the mvp and last hit bonus, and the high players are without doubt already doing that.

I'm mostly helping others for the gift rewards you get, but extra EP helps me maintain the rank i have so i get a somewhat decent reward. I do not care about the top rank, but i still want to maintain a decent one when i have the chance to.