who was the first opponent of pac in his prime?

I think Hatton was the first. Today's Pac would have stopped Diaz in the first 6 rounds.

Wasn't Marquez in his prime the first time around? I mean that would explain why he outboxed Pac so much more efficiently and pushed him back with every shot he landed. If not for the knockdowns, it would have been an easy decision for him.

I agree. Pacquaio had outgrown 126 and 130 and IMO was cutting massive amounts of muscle to make those weights. At 130, he was just dried out, but not cannibalizing his muscle tissue. That's when it all came together for him. BTW, I think he would be at his best at 140 or possibly 135 even now.