It's just that if you can't cover, then you are going to get burned when you blitz or when you rush four. I would have preferred that Eberflus sold out with the blitz when it became clear that rushing four was not going to work. Instead, he tried to zone away the coverage problem because he believes in the zone scheme.
To me, this was the biggest failure with him. It wasn't that we were going to suddenly turn into a great defense if he blitzed and designed/disguised them well. But it was clear that we didn't have the personnel for great man or zone coverage, so the only real choice was to try to bring pressure. What we would have likely have seen were some really big plays by offenses, but we saw those anyway.
Eberflus would have fared better than he did here with what he likes to do with the personnel he would have had in Seattle, but it's hard to say how much better. He's had top-10 defenses before when he had the personnel for them. But some coaches are much more dependent on personnel than others.
Eberflus had to go because he did not show the ability to adapt to what he had. There have to be signs that if the team gives you the talent, you can shine with it, and we saw no signs of that here.
So I guess that's the long way of me saying that I 100 percent agree that coaching puts the talent over the top. It maximizes what you've got. We didn't have much last year, but Eberflus also did not maximize it IMO.