Pacquiao only had 1 fight at 147 before fighting Cotto & it was against a washed (& drained) Dela Hoya. He then went down to 140 & destroyed Hatton for the IBO & Ring titles. Cotto was his first real test at the weight. The HBO team (particularly Lampley & Steward) crowed about how Pacquiao would deal with Cotto being bigger & stronger than him & how he'd take his power. Cotto was a hard puncher (particularly to with left hook & to the body). He hit harder than Marquez. He was also bigger. I'd also pick him to beat Marquez convincingly at 147. He hit Pacquiao with a lot of big punches early (despite of the 2 KD's he suffered). Pacquiao was never really hurt in the fight, just buzzed a few times. Later down the line, Marquez fought Pacquiao 2x at 147, stopping him in the final fight. How did Pacquiao's chin hold up against Cotto, but not Marquez?
It is kinda weird, especially because Pacquiao was hurt several times and even stopped at lower weights than 147 and wasn't really built for that division with T Rex arms and a height disadvantage. The thing about the Marquez KO, it wasn't a normal right hand. Not only was it a devastating counter punch Pacquiao ran right into, Marquez had the timing down after lots of sparring (there's footage on YouTube of him landing it) and having shared the ring with Pacquiao 3x previously. There was muscle memory, not to mention the burning desire for revenge. Marquez put every ounce of weight and effort into that punch, probably channeling the spirits of his Aztec Warrior ancestors lol. It wasn't as if Pacquiao just ate up the same type of punches dozens of times unfazed in their last 3 matches. There were also suspicions of Marquez being on PEDs, but I lean more towards that being damage control cope from Pac fans.
Marquez fan here… they were both on roids, PAC got hurt more at the lower weights because he was naturally a lot bigger then people want to let on for the sake of the myth that he was “actually” a flyweight lol.