Did very well at Burton
Did very well at Birmingham and stupidly sacked.
One season at Derby where they finished in the playoffs
Sacked after 8 months
I wouldn't say he's 'proved' he is rubbish.
Actually that is fair comment. But given his record at Derby and Stoke I'd have to say he doesn't look like an appointment for a club with a realistic hope of promotion from the Championship. He might do a job at, say, Ipswich or a league one club.