1. The scheme is inherently passive.
2. We just got done with three years of it.
3. IF it works, it's a statistical anomaly. Most teams that reach conference championships have a statistical correlation between league rankings for Defense DVOA versus Defense points per game allowed. Fangio defenses typically rank higher in defensive points allowed than in defensive DVOA, BUT very few teams with such a variance make divisional playoffs.
By the way, this year, of the four teams left, only one has rankings in the two stat categories that don't correlate: The Lions.
1. That's a misconception. For starters, the 2 high shell things is a relatively recent iteration of Fangio's defenses. As I've said before, he has a long track record of success in the NFL and his defenses have not always looked the same. Secondly, people think that a 2 high shell means that you always play an umbrella coverage with light boxes, but that isn't true. The shell is just the pre-snap look you present to the offense. Post-snap, these defenses can flex into a huge variety of looks. That's the whole point. Pro Football Reference has the Dolphins at 27.7% pressure this last season, which is 3rd.
2. If you watch what Fangio's defenses have been doing in recent seasons and compare it to Barry's, it wouldn't bear a lot of resemblance. Barry's problem was most implementation, adjustment, and play-calling. He was trying to operate a defense that he had all of one season's worth of experience with.
3. I think that's quite a reach. I don't pay for FO's DVOA rankings so I can't really interact with the claim.