What little power he displayed at Dayton, evaporated over the next two seasons. His development as a leadoff hitter IMO quashed his power as the organization emphasized an approach that made his power secondary at best. Had he not made the Reds out of ST, that same development path may have continued. BTW, that old adage is silly. It's an outlier adage when scouts/coaches like a skillset that hasn't really made itself known. Will Michael Stanton's HR's be longer once he gets called up? Of course not.
Stubbs problem wasn't that he didn't hit the ball hard, his approach to hitting period was flawed. Now that he's not as concerned about getting on base, guess what? he's getting on base. It's building his confidence. He's still drawing BB's, but now pitchers are respecting his power. I've only managed to see a few games, but he looks different at the plate batting lower in the order. I can only guess why, and maybe its just a small sample size and he'll go back to being the player he was in April/early May.