It feels pointless to be talking about 2018 Cam Newton, since that guy no longer exists. I agree his 2018 was not much worse than Bridgewater. But then he missed an entire season, and what the Pats saw from him in 2020 was way worse than what Carolina got from Bridgewater. Bridgewater was just ok this past year, and that would be a huge improvement over Cam. Simply put, they cannot go forward with Cam Newton as their starting quarterback. That's a season killer.
You're missing the point... which is that paying big money for a QB who isn't good just because you think he'll be marginally better than the not good QB you recently had is the worst thing you can do in the NFL. It's not that Bridgewater wasn't a decent bet to be better than Cam in 2020, it's that CAR spent a whole lot of money on QB hoping to be better than 2018, but instead they got similar or worse production to 2018 and now they're reportedly already looking for a new QB. They burned 2020-2021, tied up cap space and got poor QB production, because their entire thesis was dumb, you don't pay big money for low upside QBs just because it is better than what you have.
Cam Newton isn't good. But he's cheap, and if he's your QB it's bad, but it also means you can spend money on other positions. If you instead give 12-20M to a different bad QB, you have a worse roster, and a bad QB, even if it's the 25th best QB in the league instead of the 27th.
Cam Newton should not be the first choice for 2021 Patriots QB, BUT there are worse things than him coming back, so long as there is some idea on the longterm plan (draft?) The idea that a slight upgrade at the QB position is a definite good thing is a fallacy, and a dangerous one. I'd rather have Cam cheap for example than Foles at a lot of money (or FItz, or a number of other QBs who are bad and will make over $10M a year). Having a bad QB hurts you for that year, getting a bad QB on a bigger contract hurts you long term.
Edit- to be more clear.... the best way to build a good team and maybe win a Superbowl is to have a QB who is both good and cheap. The worst way to build a team that is good and could maybe win a Superbowl is to have a QB who is neither good nor cheap. Cam Newton is not good, but he may be cheap. If we can find a QB who is actually very good, we should get him, if we can't find a QB who is very good, we should find one that is very cheap.... Cam seems a good bet to fit that description. If Cam is the very cheap QB the coaches want, I'm fine with that.