He's probably defensive because he hears the 'do or die' music playing real loud right now. The window on Josh's rookie deal is closed, he's been provided good rosters the last couple of years and has had all the tools he needs to get it done and the team keeps coming up short.
Him launching into that unprompted is very likely an effect of this conversation being had with him by the Bills org behind closed doors.
Is he a good coach? Absolutely, he's a tremendous leader of men and a great 'get the culture right' guy.
Is he a Super Bowl winning coach? That one is looking increasingly more dubious.