You have to penalize Manu for not actually playing 35+. It's nice that he is ridiculously good in 30mpg, but thats like 7-8 mpg less than the average all star, minutes that he should be on the floor making a difference offensively and defensively. His PER would definitely shrink if he had to play 35-36mpg. How much? Who knows, but the PER does show that he is underrated if you compare him to guys who probably have a PER of 16-19 but just play a huge amount of minutes, get a large amount of shots while playing average defense....
I don't know if its fair to say Manu is better than Michael Redd or Ray Allen because those guys have to shoulder a lot of their teams offense, and they play a huge amount of minutes. Same for guys like Pierce, Carmelo, and Iverson.
Manu isn't really better than any of those guys, he might be on par when they are having 'OFF' years, but you can't say for certain he is the superior player. Maybe a more efficient 2nd/3rd gun, but that doesn't neccesarily mean he is the superior player.