Clint Barton was a criminal, and though reformed and proves himself to be a great Avenger, he still has some flaws to his character, and, his body isn't as durable as Steve Rogers. I question Bartons organising ability. When it came time to do something about Norman Osborn, Barton went in full guns blazing with no plan. He has a major chip on his shoulder and is full of self doubt. As a technician, Clint Barton has great gifts, and can turn a battle. But as a leader even his former wife, Mockingbird, chides Clint for being stupid, and that's not what is needed as a Captain America. Even when Fury handed Barton Caps shield, he rejected it, maybe because of his own self doubt, but I feel he knew himself that the role didn't fit him.
Are any proponents out there that have any strong arguments for Clint Barton as Captain America? His stint as leader of the TBolts? Does that show any leadership abilities? I found his leadership in TBolts to be mainly reconciliatory, to try to hold the team together, rather than show strong aggressive leadership. He was a bandaid rather than a dictator. For instance, why would Tony Stark think Hawkeye would make a good Captain America? Tony had seen Bucky Barnes, but Tony picked Hawkeye. It wasn't till Tony got Steves letter that Tony gave the shield to Bucky.