But Pcman fights southpaw and Cotto orthodox. Does this give either man advantages or do you think left-handers should be fighting southpaw always?
It gives a Cotto an advantage. Pacquiao's key is the straight left hand down the barrell, and to get into position to throw it he has to keep his right foot outside Cotto's left and move to the his right. Doing that takes him away from Cotto's right hand aswell, but puts him straight into the firing line of that left hand. What Pacquiao needs to do to win this fight is use his right hand more. Pump the jab when he can and move, and utilize that right-hook that he used against Hatton. Principly because Hatton and Cotto are similar in that they are both primarily left-handed fighters. Using the right hook means Pacquiao can move away from that left hand.
In a way it's also a disadvantage because book truth is that the best weapons against unorthodox fighter are straight right and right hook and Cotto being lefty is less good in these shots. It's always difficult to fight a southpaw but Cotto have fought quite a few so he should be ok.
The key is getting into the position to set-up either right-hand or left-hook with combinations. You ideally want to lead with the right-hand, which I think Cotto is capable of doing, and then link that into doubling up on the left-hook to body and head. Cotto has great composite punching skills, he can link punches to body and head no problems. That's the key to beating a southpaw. The right-hook isn't at all a weapon because it leaves you wide open for a straight left hand down the barrell.
You may be write, but just a point. I write with my left-hand, but I'm primarily and orthodox fighter and do everything else with my right hand. Plus my right eye is my dominant one, so I'm technically right-handed even though I write with my left. Pac is probably in the same boat as me.