Everybody wants one punch knockout power but as the saying goes "every rose has it's thorn". When you look at most of the best fighters of all time most relied on skill not power (exception: Sugar Ray Robinson had skill and power).  The problem with having tremendous power is that the fighter will tend to rely on his "big" punch instead of developing his all around game. It's just human nature. If you take a rich kid who knows he's a big inheritance coming generally it's hard for the kid to be motivated like a kid that doesn't have that kind of guarantee. When go through the history of boxing most of the greats weren't single punch KO artists. Look at the game today Andre Ward, Floyd Mayweather neither have deadly  power but they have off the charts skill. Why, because they were forced to develop it. Now take a look at Pacquiao, skill wise he's leaves a little to be desired but he has a left hand that can ICE anybody. More than likely coming up in boxing psychologically Manny knew his punch could change any fight so instead developing different skills he was more concerned with finding a way to land the big left hand. Much has been written and reported about Freddie Roach developing his right hand. Why would a world champion not be able to punch with one hand? That's because the other hand has other worldly power. Manny is an exceptional athlete with alot intangibles so he has still been able to climb to the zenith of boxing but the vast majority of big punchers never get that far . Largely because they solely depend on their power.