Coaches matter a ton, though their impact is felt more over time than some fans tend to think and less on a game-to-game basis. I'm a bit on the fence about Marinelli, overall, but there's no doubt those players in CHI loved him and credited them with their success, pretty much directly contradicting what you're peddling here.
"Tillman: Can I say one thing, real quick? You guys are so blessed to have Rod Marinelli. That guy is the best coach, defensive coordinator in the National Football League. I've had some of my best seasons when he was my D-coordinator in Chicago. You guys, Cowboy nation, I'm telling y'all - you don't understand how much of a gem that this guy is. He is a steal. Y'all need to give that man all the money. He is so valuable to his team. He is just an awesome guy.
How much more talent does Marinelli need to get the defense to the next level?
Tillman: I want to say this in a respectful way because I think the Dallas Cowboys defense, they're good players, but they weren't household names. They were names people didn't know, and look how amazing they did.
Now, I think if he had just a sprinkle of talent, they probably could have taken it a little bit further ... Rod Marinelli reminds me of Bill Belichick. You look at Chris Hogan, the guy played lacrosse, and then he goes out and has a career day. I'm looking at Danny Amendola, Julian Edleman, these are just normal guys - 5'9", 5'10" - but they're quick. They're not fast. But they go out and they make plays for them. Rod Marinelli, he does that with defensive guys all the time, and I think he's done it in Dallas the last couple years ... So, give him just two or three more guys, athletic, fast, and he can do it all.
Then again, I've been beating the drum for more talent on defense for a very long time at this point. I'm not arguing we have talent. The defense stinks. But we do have a scheme that's supposed to produce turnovers, and a coach that's well-known for having defenses that product turnovers, and recently, in the NFL.
The issue has been that we have had poor LB and S play, and that our front has been missing their run fits and tackling poorly. Those last two things do happen to be coaching issues, btw, so it's not like there's not enough blame to spread around for the lousy defense.