20 or higher is bad. Like fireable bad. Pick whatever parameter you want.
Go ahead. Look at these and tell me they were comparable in success.
http://www.pro-football-reference.com/coaches/RyanRo0.htm
http://www.pro-football-reference.com/coaches/SchwJi0.htm
Schwartz years average defense (16th) or better. 7/15 years in the NFL.
Robbie years average defense (16th) or better. 3/12 years in the NFL.
With Rob Ryan, the rule is your defense isn't just not going to be good, it's gonna to SUCK. It's sucked 9 seasons he's been a DC. He's only had an above average defense 3 times in his whole freaking career!
What is the difference between no sustained success and sucking?
Yep. I used that this time. By any parameter, Rob Ryan has been bad, and worse than Schwartz.