Van Gorder going away simply improves the defense 100%. We'll see better effort which will hopefully lead to better execution. This year wasn't just bad. It was historically bad. The Cards broke all the wrong records. No way they play close to that in '19.
I agree that BVG was historically bad, and that a competent DC can make a huge difference, but I'll also point out the following:
D-Line--If it turns out to be true that Jon Greenard is leaving, there will not be a legitimate ACC starting defensive lineman on the roster, not one!
LB--A solid core to build on. CJ Avery, PJ Blue, and Dorian Etheridge have talent and ability. I also like Yasir Abdullah to be a stud down the road.
Safety--Tresean Smith is the only legit safety on the roster
CB--Rodjay Burns showed promise, but is not a lockdown kind of guy. The rest of the corners are warm bodies.
I don't care who the DC is, you can't field a solid defense with linebacker being the only place you have talent.