McCarthy hired Dom Capers and Mike Pettine as his DC's while in Green Bay. Capers of course did a great job with them for several years and Pettine is still there as the DC and running their defense, which has been the main reason for their turnaround.
Those are some pretty solid hires.
Nolan has been the LB coach in New Orleans for 3 years and I think has done a very good job with their group despite not having any truly elite players. Demario Davis has always been very talented but bounced around between a few teams, the Saints signed him as an unheralded FA last year and now he's 1st Team All-Pro in just his second season there.
He's been in charge of some very good defenses and some very mediocre ones, and if I had to guess it'll mostly come down to personnel. If we can consistently give him talent similar to what we had in 2019, adjusted based on his personnel preferences, I think he'll be fine.