First, one has to admit the team's weaknesses.
1) there are no stars in the secondary. Is undrafted JC Jackson a true number 1? Are any of the safeties better than average? Is the slow corners effective with Jones out for the season? Mills, Williams, Wade...these are all unproven CB's who have struggled in their career.
2) the LB's are old and slow
3) there are no elite weapons on offense, certainly not like the kind you usually find on contenders.
4) they are unlikely to get a first-round bye.
But here's why they are contenders:
1) the combination of McDaniels with a QB like Jones and a diversity of weapons is lethal. The key to success in the NFL is to be unpredictable. Years ago, Bill Cowher built a powerful Steeler team with a different philosophy. "We do what we do," was his motto. That succeeded in creating a culture of toughness. We're going to assert out will over you and there's nothing you can do about it. Think of Larry Bird at the end of the game telling his opponent where he's gonna shoot from then doing it.
But you can't win titles doing that. You're giving up too much in telling the opponent exactly what you are going to do, and Pittsburgh kept getting beat in the playoffs...until Cowher learned the lesson and became unpredictable. Then he won a champtionship.
On any given play, you usually have no idea what the Pats will do. Dropping back to pass in shotgun? Uh oh, here comes a screen pass, which is basically a run play. Now, every team does this to a degree. But in order to be really good at it, you need the right pieces, most especially the right QB. I liked Cam Newton, but he was a waste of McDaniel's creativity. His short passes were inaccurate and poorly timed.
But Mac Jones is already demonstrating a masterful ability in this. Many fans and sportswriters don't really appreciate what they're watching. The decisions made pre-snap and right after the snap, the touch on short passes, the timing and patience to allow a play to develop.
You don't the type of weapons KC has for this. But those weapons are expensive. For the Pats offense, you need a White, a Bolden, a Jakobs...even a Harry, who is an outstanding blocker and is becoming quietly essential. You need a possession WR like Meyers. You need a surehanded TE target. You need some WR's with just enough speed to keep defenses honest, and a thoroughbred running back or two.
The Pats don't say "we do what we do". They say "we do what you least expect". And it's very difficult to stop.
2) for 12 years, the Belichick defense sucks in Sept, kinda stinks in October, is mediocre in Nov. By December it's looking good. And in the playoffs, the defense can be a difference maker. To get there, they've needed a high powered offense that can win close games, and a weak division.
Doesn't that look like exactly what we still have? The offense, with its rookie QB, had to grow a lot through the first half of the season, so it was a rocky start. But the division is still weak and they are in the position to at least grab a wild card. Had they drafted Jones a year ago, one can speculate that right now they'd be 9 and 1 or 8 and 2, poised to capture that bye, and it would look very much like peak Brady.
The road probably goes through Tennessee because they have the best record and a very easy schedule. Baltimore has a tough division and brutal schedule, as does Pittsburgh. We'll see what happens with Buffalo. On paper, they might be best in the conference, but that stinker against Jax is not out of mind yet. Let's say the Pats split with the Bills, beat Miami and pick up one more loss, maybe Tennessee. All they would need is for Buffalo to lose 2 games in addition to the Pats loss. Both teams would end up with 6 losses, and I believe the Pats have the tiebreaker. That's not a crazy possibility. Of course, better for the Pats to split with the Bills and win the others. I do think they probably need to win the division to be serious contenders. But the Pats are undefeated on the road, so it's not impossible for them to make a run from the wild card spot. However, they haven't done that since 1985.