The group mission achievements are good XP. The regular progression rewards are not good exp for the time spent compared to grinding. I've done progression on about a dozen alts. I have another 10 that haven't done it and had no desire to do so. I find progression tasks mundane and boring and don't appreciate being forced to do EoK progression so that I can play some of my lesser cared for alts in RoS zones without being blown up. Having to avoid a few areas of Lab in EoK was a reasonable compromise. There are also some classes which the Hero's AAs do diddly squat for.