I feel you but no. They clearly have a leader-subordinate relationship. When Madara instructed Pain to get the Nine-tails, he also told him "I will NOT ACCEPT failure." That's not something you say to a co-leader. You say that to a subordinate. Madara later went on to COMMAND Pain to tell the others to hurry up and capture their beasts. http://www.onemanga.com/Naruto/364/16/ Finally Madara says "soon our goals will be achieved, then the sharigan's true power, my power, Uchiha Madara's power..." It's as though all of Akatsuki's goals benefit Madara the most. After all it was Pain who joined Akatsuki and acts as the front man. It's not the other way around. Most of the members didn't even know that Madara was even in Akatsuki let alone the real one pulling the strings.
Pain defeating Hanzou is nothing. Any ninja with Pain's abilities could've defeated Hanzou. He controls six bodies with unique abilities that he can continue to revive because he can only be killed in a special way. The fact that the Sannin lost to him was most likely due to the their relative inexperience at the time.
The flaw in that theory is simply that if age and experience were the true deciding factors, then Kakuzu could've just as easily have been the leader since he is just about the same age as Madara. Remember he too encountered Shodaime.
And if you are willing to admit that Pain may not have "reached his full potential yet" you are also admitting that Pain is weaker than Madara. You are saying that Madara is seasoned while Pain still needs more growth, and the implications of that are simple: Madara is more powerful than Pain, which is why he's the true leader of Akatsuki, a point that I made initially. So thanks for agreeing with me. XD