I personally like MW5's version. The guns have a slow reload but not the damage reduction
I honestly have issues with the way PGI depicted the Heavy Rifle and the Chemical Laser, they just made the another variety of Auto-Canon and Laser to hunt down with the Heavy Rifle now a light weight AC/20. The TT doesn't do rate of fire well, a simulator on the other hand; an AC/20 that's nearly half the weight, just a little more wait between shots, Clan tech is almost a side grade now. I understand PGI needed to sell their DLCs but that depiction of Rifles felt more like a fan mod akin to MekTek's RAC 20s.
Yes, quadrupling the barrel's thickness does let you fire higher quality shells.
Innovation!
Keep in mind that in real life; the AC/5 came first, followed by the AC/2, AC/10 and AC/20, then Ultra AC/5 and LB-10X, ect. If anything, your complaint is that CGL should have made the Heavy Rifle suck *more* when they created Primitive tech for the Time of War setting.