Marinelli is not a genius; he's an excellent coach when he has the pieces that he needs because he teaches technique, assignment-sound football and can motivate players. He was a great defensive line coach when he had players like Booger McFarland, Simeon Rice and Warren Sapp in Tampa. His Bears defenses from 2010-2012 were stout, but they had Tommie Harris, Julius Peppers, Henry Melton, Lance Briggs and Brian Urlacher, and it's hard to tell how much of a role Love Smith played with those defenses.
So the argument could be that if you give Marinelli great players, he can produce great defenses ... but that argument could be made about a lot of DCs. If you are not going to load the defense with great players, then you need to have a more creative coordinator who stands a chance at confusing the offense instead of depending on his players to just be better than theirs.