Are you worried that he's coming to TKO Spence? Kidding aside, he never had one punch KO power in WW, more of one punch flash KD power due to the weird angles. Last legit KO he had was against Hatton. So I'd say his single punch KO power got maxxed out at JrWW.
The idea that anything happened to it isn't really based on anything, like a lot of things boxing fans think.
I still think he has the same one shot power as before. But he no longer fights with the same intensity and pace. He used to be just all over an opponent, forcing them to make mistakes and then he'd catch him with a shot they didn't expect and they'd be hurt and go down and then Pac would go up a gear and eventually finish them. Now with the lower work rate his opponents are less likely to get caught unexpectedly. When they do they still get hurt or go down but Manny can't just then unload non stop to press that advantage and eventually force a stoppage like before. So he has less opportunities to end the fight and when he does get an opportunity he can't maintain the pressure for round after round like before to break guys down, he has to step back and give his opponents time to recover.