I agree with you that I would also build the offense and defense starting with the lines then the quarterback and pass rushers after that.
I have always thought the best cornerbacks are sets of cornerbacks, not individual cornerbacks.
It's why I don't want to draft cornerbacks in first couple of rounds nor do I want to trade #1 or #2 picks for them.
While it's great to have a top 5 cornerback on your team, that player is one injury away from dropping you from a solid defense to worst in the league.
What I want are a set of 3 solid cornerbacks that can play man, always stay within 1-3 yards of the receiver they are convering and most importantly tackle aggressively (not chase tackle).
I am also more concerned with PBUs over interceptions because PBUs can happen every game while interceptions are random and spread out and many happen from tipped passes or receivers running the wrong routes.
Having 3 solid (not great, but solid) cornerbacks makes your defensive backfield hard to beat consistently downfield.
For 30 years, the Cowboys have relied on pash rush to create mistakes for the secondary to capitalize on but there is one weakness with that concept and it has cost the Cowboys many of those failed 30 seasons when they ran up against it.
That weakness is a great offensive line or at least great offensive line blocking game plan.
That's why Quinn's defense was so hit or miss. When they got pressure, they got turnovers and the defense looked awesome. When they failed to create pressure, teams scored easily and often.
I said during off-season that it would likely take half a season for Parker to get this defense working (assuming he could/can of course).
That said, if its true that his focus is on coverage-first then they should have put a lot more focus on improving the secondary and its depth than they did.
They should have also picked up at least one solid pass rusher (and Gary was never that).