I think Sir Alex was also part of the problems that befell Manchester United when he resigned. News then had it that he was the man that handpicked his successor which was David Moyes. That was the genesis of Manchester United problems, an inexperienced coach handling a team like Manchester United at that time, this was a title winning team that was handed over to him.
I don’t know much about the things that happened during Sir Alex Ferguson’s departure but the club has suffered and struggled since then which certainly tells that the management style and strategies have not been efficient and effective since then. The Glazers are the real problem gor Manchester United for their poor management style.