I mentioned in another thread a while back that Hardy often had a gassed look to him during games last year. Whether it was hands on the hips or even his body language when he'd come off the field he just looked a little out of breath, moreso than most guys do when they take a breather. This isn't to turn this into an argument over his weight or his stamina or anything, just an observation.
However, this could be one of the reasons that the FO took Kuechly instead of a guy like Coples. They may have decided Hardy can be a dominant beast, but only when his tank isn't on empty obviously. Also coincides with what some guys said about Rivera not wanting Hardy to play too heavy last year. Time will tell but I'd rather have a fresh Greg Hardy for 70% of snaps than a tired one for 90%.
Adding extra weight will not help him if he has issues with getting gassed. People see someone bulk up in the NFL and think its a good thing but most of the time it isn't.