I'm going to disagree here because that Bears offense was ok in 2018, whereas the defense was outstanding. And schematically, Nagy has never been impressive. Even allowing for a lack of talent on offense, you would expect someone who was formerly an OC to Andy Reid to be much better at play-calling. Their offense kinda improved down the stretch when they started using a lot more Play-Action under center but other than that, I don't think I've ever seen much from Nagy to suggest he's a good offensive mind.
And on the Coach of the Year thing, I'm a bit skeptical when it comes to such awards. Ryan Grigson won Executive of the Year in 2012 but all the Colts' success that season was mainly down to Andrew Luck, not Grigson. Similarly, the 2018 Bears owed a lot more of their success to Vic Fangio as DC (And possibly Brandon Staley as LB's coach) than it did to Matt Nagy.