That's what I found. I kind of liked it at first, then I loaded it with kit. Radio, spare btys, 48hrs rats, water and double frontline with minimal sleep and snivel kit put the ruck over it's limit for comfort, cut up my hips and the load in relation to the harness was so ackward it made rucking up such a pain that I usually just left the ruck on unless we were staying put for a long time.
The design would probably be alright if they put it on a diet, slimmed the waist belt up so it didn't push down on your hip flexors and added some lower back support to compensate for the gap left when wearing armour. Fully loaded I think I used less than half the available capacity...