Mac was not surprised that most of Omega turned. Why do you see this as flawed character judgement? If anything, it reinforces strong character judgement: he knew down to a person who was corruptable and who was not. Look which people were in Beta, Gamma, and Alpha respectively.
When finding beings of a given power level, you have a couple choices: You can leave them to run amok in society, or you can put them in a controlled atmosphere and measure the progress of their power even as you attempt to turn them into productive citizens.
Mac may have been a reluctant leader, but you're making a pretty good case for his having had remarkable vision and the wits to institute it. I never would have thought of that example.
[Mac] is the character that had the vision to create a national team, and create a national organization dedicated to a dream akin to Xavier's. He's the character who had the force of personality to hold the original, squabbling Alpha together -- who were, and remain, representative of Canada's different squabbling political factions, which is why they continue to "gel" and feel more right than the various Alpha creations since that time. Roger Bochs and Eugene Judd didn't just follow Mac because of a paycheck: they were inspired by him.