I wouldn't say Manny is better in general, there is only one element of Pac's style that is the issue, but it will spell doom every time they fight; that's the in and out movement of Manny.
You put a half decent MMA fighter and he won't have a chance. There's no way they would dare to trade shots with him. Takes years of experience to develop some skills in submission/groundwork, most of these elite MMA fighters have been training almost all their lives likewise with elite boxers.
lol Randy Couture stood safely 5 feet away from Toney and took a wild flying leap at the leg of an old fat washed up Boxer because he didn't even want to get close.
Manny would wreck em, especially with a little of that take down defense.