At 122 Pacquaio actually put everyone to sleep. 100% KO ratio I believe. So yes He was just like the guys you mentioned years ago.
He still hits plenty hard. As his speed of hand and foot has declined, the impact of his shots have decreased as has the frequency with which he lands them. They're easier to see coming now, as well. Still, he at least stunned JMM every once in a while in the 3rd fight when he caught him flush, rocked Bradley a few times, put Mosley on the canvas, and wobbled Margarito around the ring a few times. Manny was never this one-shot, destructive kind of puncher at 130 and up anyway. The Hatton KO was a lighting in a bottle kind of moment, literally a picture-perfect shot where everything lined up just right. Pretty much all of his ko's since stepping up from Featherweight have been of the accumulated punishment variety. Perhaps more importantly, his last few outings have been against guys not exactly known for being easy to hurt, let alone stop.
Didn't go anywhere. Pac's power was over rated by the hype train, i.e. his promoters, HBO and the legions of rabbid Pac fiends. He had good power at the lower weights when he could tee off on his opponents. He one punched Hatton later at 140, but Hatton's chin wasn't that good. De La Hoya quit on his stool without ever tasting the canvas. Cotto who had previously shown some chinnyness wasn't KO'd, the ref stopped the fight in the 12th at a point when Cotto wasn't hurt. Pac has decent power at Welter, not the great power his bandwagonists claimed though. Two observations. Pac is definitely off whatever he was taking back when he looked like the hulk. He has a little less muscle bulk and is not as ripped. Roach also wrapped Pac's hands in an illegal manner at least twice, and when that was mentioned it puts a spotlight on the issue. Roach can't do that anymore because the other camp knows what to look for now.
His pop, accuracy and overall movement speed has declined... Which makes his punches a bit easier to predict and escape from.. He has a tougher time connecting and swarming his opponents..
Manny had power? He never hurt Oscar despite landing anything he wanted and anyone can knock hype job hatton out!
The power is there is it has always been. But, the targets have not been there (in front of him) all night, like most of his opposition, since the second Marquez fight. His stamina is what has noticeably declined over the last 3 years, IMO.