I mean, I spent a season saying that he doesn't have great athleticism or a plus arm... and neither did Rosen. Darnold also had neutral to poor athleticism but a good, not elite arm.
I honestly don't even get this argument track you're on... Mac Jones has had a mediocre NFL career so far, he's still not terrible, he's just not a difference maker.
Plenty of teams will play non-difference makers this year at QB, and a lot of them will be paying more for them than Mac Jones. It's why absent a top QB falling into their lap the Patriots will start Mac and it's the right call.
If you can reasonably get Lamar Jackson (a difference maker) you do, then you trade Jones, and history has show worse QBs than Mac Jones return solid draft compensation.... including Sam Darnold. Because.... if you're a different team that can't get a difference maker at QB, but doesn't want to tear it down the second best way to contend is to get the best, cheapest non-difference maker you can and build an elite team around them (see Jimmy G in SF, Goff in LA, etc.)
If people want to argue that Sam Darnold was seen as a guy with elite athletic/arm traits 3 years into his career, they can, but that doesn't match the pre-draft and post-draft writings of the time, you can look it up they're all still on the internet. Expecting Mac Jones to return at minimum what Darnold did is more than reasonable, if anything expecting less assumes a wild change in the evaluation of QBs in the last 2 years... and there isn't the evidence for it.
DUmp him... no. But I think we've seen enough of Bill the GM to know that if he can massively upgrade his talent he's not letting past draft picks, or anything else stand in his way. He hired BOB because he needed an OC, and he didn't have one. If he could reasonably add an elite QB he'd move on from Mac in an instant. The question came out of.... if BIll wanted to do it, and Kraft opened the pocketbook for Lamar. what do you do with Mac.