I see it a little differently. It's really hard to think of things as "business as usual", when your business the last 20 years has included unprecedented stability (and excellence) at the most important position on the field. Having that as a known commodity allows for a team building strategy that just won't work with the QB up in the air for the first time in two decades.
But, I also can't see Belichick accepting a bad season on purpose, nor do I think that's a good thing in the NFL. What I see is them having a much larger chunk of cap space next year, so they're making plans to be agile when that comes. This year, the goal is to see what they have in Stidham (or another young QB, if they like one in this draft), so they know whether part of that cap space needs to be allocated to that position in 2021. The only way you're going to get a true evaluation of the kid(s) is if there's a decent enough team around him so you know what he can do as part of it.
The offense will be tough to overhaul, but they can do better than last year. If let's say they add a mid-level TE1, a WR2 to accompany Edelman, and get Andrews back at C, I think the offense is solid enough to be able to say, "Okay, with a good defense, we can win with Jarrett" OR, "Even with a good defense, Jarrett isn't enough."
Those are the primary goals this year:
1) Figure out what you already have at QB, to determine your course of action going forward.
2) Stay financially agile in 2021 so you can make a splash/keep the players you really like, and potentially sign a top level veteran QB if need be.
And, even though the schedule looks tough, this defense still has the potential to make us a playoff team, especially if the combination of Andrews and a real FB gets the running game back to a dependable level.