Well, he's not at fault for the team not winning, unless you fault him for the repeated collapses of his historically weak bullpens.
But the weak farm system and the horrific contracts he gave to players like Cabrera and Verlander, could cripple that franchise for years, especially if the team continues to play poorly, which will likely negatively impact attendance and in turn, earnings. This means their spending will be capped by the debt-equity ratio of the CBA.
So he left a team with no farm system and likely handicapped their ability to pay for free agents. Not a good spot...