If you are overleveled for the content the game scales you down (Or the content up I guess) to even out the field. I believe regardless if you were 6 levels over the content you would really only deal/receive damage as though you were 2 levels above. Hence why level 30's can still die when selecting the level 8 earth strike, and why you can't one shot all the yellow bars in that strike. Edit: Granted, new modifiers and such could be useful. Though keep in mind the only change in exp you'll see is for the end. a level 2 dreg and a level 24 dreg still give the same exp for kill.