First question: Did you wear any other weighted packs, or just the Deuter? For example, did you try the Exos on at the same time? If you tried on 4-5 weighted packs, compared them all, & decided that the Deuter was the clear winner, then it probably makes sense to stick with that pack... or go for one of their lighter models, such as the ACT Lite 60+10 at ~3 pounds.
A pack that fits better will make up for extra weight by carrying more comfortably, annoying you less, wearing on you less, and generally saving you some energy spent working against a poorer-fitting pack. That said, if you can get a pack that feels as good as the one you have, and weighs a pound or two less, changing would make a lot of sense!
Sore hips, of course, can stem from any number of issues. First question, is he wearing the belt properly? If he is, does he adjust the pack at all throughout a day of hiking, or does he always have the load lifters cranked & all the weight going to his hips all day? Part of it could just be getting used to having all that weight on the hips. I also find that a lot of people try to skimp on a pad, and their hips get sore during the night sleeping on a one-inch pad while sleeping on their side. Particularly if he's a side-sleeper, steer him toward a 2-inch pad or so... maybe like your Neo, or a Big Agnes IAC. Lastly, it could be a poor fit. Did he try on a number of packs, or just the Exos? Again, if he tried on several and the Exos felt the best, it was probably a good choice.