As far as Lee or Gai easily taking out pain, I can just see Pain holding his metal stick out and pulling their heads straight through it. Remember, he's trying to capture Naruto alive, not kill him. He just beat the crap out of three giant frogs. I think he's plenty strong to take out anyone. And it's not like his physical attacks and speed are lacking either. And he might be able to see through their attacks easier like Sasuke did with the Sharingan. Rinnegan probably works better, too.