Marinelli's scheme is about getting to the QB. He doesn't play a typical 4-3 scheme like a Mike Zimmer or Marvin Lewis where you have a tradition 1-tech that clogs the hole, plays the first 2 downs and have the more dynamic 3-tech get a little more space.
Rod wants every D-Lineman to get up field while maintaining their gap responsibility. He wants a Booger McFarland type at the 1-tech instead of a Willie Blade type.
The issue we are finding these days is that the modern game has changed from even 10 years ago. Pass happy, shotgun offenses that throw the ball out on perimeter for short, quick throws. The vast majority of the best defenses are built from the defensive backfield to the linebackers to the D-Line. The Seahawks are a perfect example of that as their DB's (when healthy) are excellent and Wagner and KJ Wright are stupendous. Same with the Panthers, Patriots, Cardinals, etc.
That alone should place a little less value on D-Linemen.
And now, the big emphasis around the league is getting pressure from the inside because with the shotgun offenses, it's a bit harder to get that pressure from the edge. You also have more mobile QB's that have perfected the spin move (ala Romo) to avoid those edge rushers. Your edge rushers are better served to be guys that can get the occasional pressure, not lose outside contain and have the motor to go chase after the ball when the QB throws it quickly. Unless you have Von Miller and there's only 1 Von Miller in the league and nobody else is really close. That means more of an emphasis on interior D-Linemen and the guys you really want are less likely to be available.
Lastly, most consider Marinelli as the best D-Line coach on the planet. I tend to think he's really great, especially with DT's. And the general belief is that they don't need to pay big $$$ for a DT when Marinelli can 'coach them up.'
I wouldn't mind seeing us draft a real game changer at DT if he's there, but I don't think the DT position was a problem for us. Irving was really good, he just didn't get a lot of snaps. McClain is solid, but wore down as the game went along. Collins showed real flashes, but also looked bad at times. Thornton got better as the season went along. And while I'm not high on T. Crawford, I don't think one can judge him based off of 2016 where he was playing completely out of position.
Our DE's were a much larger problem.
YR