A lot of the old timers believed Griffith was a dynamic puncher before the Paret fight. The Paret fight took a lot of the aggressiveness from Griffith. He was not the same (he actually said so himself, but who really could be, unless you're psychotic) . So I would say after Parent, Hearns wins decision, maybe a late tko, before.... Toss up.
I think Griffith may very well have stopped Hearns...he was a dangerous puncher more at welter than at middle, and he was stronger than Hearns....plus he was clearly the superior 15 round fighter.