He did well at Spurs and hasn't done since, yet continues to get touted for top jobs. He's also made two poor choices in the team's he has chosen to manage. No one made him take either job. Aside from one spell at Spurs, which is quite a while ago now, I haven't seen anything from him to indicate that he's a top manager.
Ferguson, Pep and Ancelotti, to use your own examples all had more than enough credit in the bank to excuse those 'isolated mistakes', which didn't span years and multiple clubs.