The only way you find one is to keep drafting and playing them. Cardale for the rest of the year, then draft one of the guys in the next draft. Like you said, it's a crapshoot, so saying "x is gonna be great" doesn't mean much. Grab a number and see what happens.
Rex clearly set the standard of success. That's what matters. No matter how much a "slightly above average" defense is defending by fans on message boards, by Rex Ryan's opinion, that's not good enough.
This team is nationally relevant? How so? As being Rex's band of fools?
This team was nationally relevant when we had tons of defensive stars make Pro Bowls and All-Pro teams.