It's really hard to predict how coordinators will turn out, like this Brandon Staley guy in LA, nobody would've been excited about him based on his track record but he's apparently a great defensive mind and likely to be a HC in a year or two, if not next month.
All we can do is hope for a position coach from an accomplished defense (Ravens, Bills, 49ers, Steelers, etc.) or a former HC with an accomplished background as a DC.
Obviously that's what Quinn is, he never got the defense stabilized on an offense-centric team in Atlanta, but you can't lay that all at his feet. First, he's not the coordinator, and secondly, he's not in charge of talent acquisition, and even with all that said their defense was trending upwards in 2016 with young guys like Grady Jarrett, Deion Jones, Devondre Campbell and Vic Beasley, they dominated the Patriots in the first half of that Super Bowl, and then the second half happened and the entire organization never seemed to recover.
I mean, from what I remember they thoroughly dominated Brady in the first half with relentless pressure, they scored a TD if I recall correctly, and then they went into safe-mode in the second half trying to run out the clock, which is fine up 28-3 with like 22 minutes left in the game. If not for a historic set of circumstances, some flukes, and some ridiculous play-calling on their last offensive drive it would've worked out perfectly fine and Quinn would almost certainly be the HC in Atlanta as we speak.
So yea, long story short, it's not some kickass yeehaw grand slam, but it's about as well as you could hope for.