We'll see when the season is over how things shape up. Getting back to the Giants, in 1985, they allowed 21 or more points 7 times . . . and lost everyone of those games. They gave up 35 to CLE (9-9) and another 35 to CIN (7-9). I don't really consider that version of the Giants defense all that intimidating.
The 86 defense was much better, but even that team allowed 31 points to a 7-9 Cowboys team. They allowed single digit scoring totals against the 4 win Chargers, 5 win Eagles, and twice against the 4 win Cardinals. Bottom line, good defenses beat up on a bunch of inferior opponents all the time. It's not unique to the Patriots.
As I pointed out in other threads, even teams considered all time greats had bad weeks. The 85 Bears allowed weeks of 38, 28, and 24 points. The 00 Ravens allowed Marc Brunell and the 7-9 Jags to throw for almost 400 yards and score 36 points on them. Vinny Testaverde torched them for almost 500 yards that season.
Like I said earlier, history remembers the good things and glosses over the bad things. If NE were to solve some of their offensive issues, the defense keeps forcing turnovers, and the Pats win another title by beating the Chiefs, Ravens, and 49ers and allow only 30 points across those games total, there will be a completely different narrative written on the Pats defense. For the record, no, I don't think that will happen . . . but it is way too soon to tell the story of the 2019 season. The Ravens look great now, but if the Ravens are one and done in the playoffs, their storybook season may not end up being so storybook. While there may not been many weeks left to this season, the most important weeks are still to come.