I mean, I don't think it was overrated despite making jokes about it.
The Vikings and lions won a combined 29 games. Their winning percentage outside of division was as good as intradivision. you don't win 29 games without being very good. Hell, even the packers only lost one game outside of division play.
they just lost two games. I don't think this means they were overrated.
It is an interesting question, particularly in light of the horrific postseason performance by the division.
Not counting the Playoffs, the Vikings, Lions, and Packers were a combined 29-4 outside of the division. Objectively, that is a tremendous record, particularly given parity in the NFL is so great. Quite frankly, you are probably right. Teams are what their records say they are in the NFL. 15-2 and 14-3 are two of the best regular season records in NFL history, and 11-6 is a very good record. That all three records were put up in the same division is extremely impressive.
The counter is that the NFC North matched up arguably the worst division in the AFC (AFC South, consisting of a mediocre team (Houston) and three poor teams (Indy, Jacksonville, and Tennessee)). The Vikings, Lions, and Packers went 12-0 against the AFC South. Each team played 7 other non-division games in the regular season. Against teams with a losing record, the Vikings, Lions, and Packers went 12-0. Against teams with a winning record, they went a combined 5-4. Against non-division playoff teams, they went a combined 2-4 (and of course, if factoring in the playoffs, went 2-7).
Ultimately, I think it is probably not fair to say that the NFC North was overrated. Detroit was a great team. They easily could have won the Super Bowl, but saved a stinker of a performance for their most important game. I believe Minnesota and Green Bay were probably a bit overrated in comparison to their records. Minnesota was a high quality team, and while I did not believe they would win the Super Bowl this season, I do believe they could just as easily have been in Washington's shoes if matchups had shook up just a bit differently (Rams were a terrible opponent for the Vikings). Green Bay was a slightly above-average team. I'm not a believer in Jordan Love, and I think the Packers reached just about their pinnacle with Love at the helm (9-11 win team that can make the playoffs, but likely a Wild Card exit). That being said, if Green Bay is your third best team, your division is pretty good.