He didn't have the personell to be successful, you could of put any DC there and they wouldn't of done good. NO took the best on the market which was Spags to try to get something out of the slow and old D, not even Spags could.
There's a difference between not doing well and being the worst defense in the history of the NFL.
But he hired and fired him in one year. He obviously didn't like what he saw/heard.
Sure, if Spags had run a great defense this year he wouldn't have been fired, however, you cannot make the claim that a great coach fired him. Payton never worked with him and then decided to go in a completely different direction defensively.