I don't think Lewis was a bad hire. Problem the Bengals did is kept him on too long. Had the Bengals got rid of him in 2015 after losing another home playoffs game this following a 12-4 season then the criticism of the Bengals wouldn't have happen. There was no reason for him to be there 3 additional seasons after that.
Yes and no. Failing consistently in the playoffs (especially at home), can definitely get a coach fired.
But at the same time, it's hard to justify firing a coach who went 12-4.
Sometimes the problem is that the coach hasn't been given the final pieces he needs to get the team over the top. I saw that in the 80's when I was still a Rams fan.
On the other hand, sometimes the coach has taken the team as far as he can. We saw that in the 90's with Del Harris and the Lakers.
Was it more 80's Rams or 90's Lakers?