In a chat with ESPN UK, Arum concedes that had the fight happened six years ago then Mayweather would have been a tough opponent to beat.
But now Arum feels that Pacquiao is a more complete fresh fighter, moving better and generally throwing more, better punches overall.
Arum knows Mayweather well as he fought under the Top Rank banner until 2006 before leaving to fight as a free agent.
"He's better than I've ever seen him. I really think Manny's going to stop him [Mayweather].
"Mayweather's an excellent fighter, no question about that, and he creates a tremendous challenge for Manny.
"But I think Manny at this stage can rise to that challenge and win the fight," Arum told ESPN UK.
"I think he has the better skill set of the two at this stage in their careers. I think he'll win with movement, by the number of punches that he throws, and I think his foot speed is a lot better," he added.