I don't think he's a terribly good manager. He's average to below average at best. I don't blame him for everything like most do, but his style, particularly on offense, is grating, boring and now ineffective. Maybe he didn't need to be fired "long ago", but certainly at the end of last year.
That team clearly got stale and things no longer were working offensively. Same thing happened with Gardenhire. It was obvious when things got stale when he was in charge and ownership refused to acknowledge or care and kept him on for years after. He should have been let go even if it was just to shake things up.