Maybe.... I am not entirely convinced at this point that Newton is the week 1 starter.....
I think he will be.
I don't see the 49ers letting go of Jimmy G for a third rounder or something like that and then trading away what it takes to get Watson. Seattle probably won't trade Russell Wilson within their division. Now maybe there is a slight chance Niners gamble on Sam Darnold over Jimmy G but I doubt that.
And no matter who the Patriots draft, I would think Belichick gives that player at least 6-8 weeks and probably more as the backup to learn the Patriots scheme. I doubt Patriots pay the high price it will cost to get a DeShaun Watson.
He was a good QB - he now is unable to throw consistently, has a very slow windup, does not process the field well, takes too many sacks, throws the ball into the dirt, can't hit the short stuff, is fairly inaccurate overall (ball placement is terrible), and gets too many balls knocked down. You point to his rushing TDs, I suggest a RB could get those TDs too - How good do you feel about Cam at the 10 yard line getting a TD? Not very good. Let's add cannot recognize the blitz, cannot read defenses, and never once used motion to diagnose whether it was zone vs. man defense.
Cam is terrible, he is the worst starting QB in the league - Tyrod Taylor would be a giant upgrade.
A running back could not get many of those TDs. Cam isn't running in to inflate his stats, he is running in since he is actually the best running QB in NFL history until Lamar Jackson. Often easier for defenses to stop a running back near goal line that a big powerful fast QB like Cam Newton. And Newton with his running ability, also makes it easier for the running backs to run.
Very few running backs run for 12 TDs nowadays.
You are mostly right about Cam's mechanics but he had bad mechanics when he was winning the MVP and going 15-1 as well. The guy was never a great pure passer.
The part that you are missing is Cam's ability to run the ball gets his receivers more open than they would be with a pure pocket passer like Brady or even a QB that scrambles and can run a moderate amount like Aaron Rodgers. Even Russell Wilson doesn't scare teams like Cam Newton running the ball. Wilson may pick up plenty of yards but he isn't a threat to over run a defensive back so it is tough for defenses to go small against a team with Cam.
I believe running ability for most quarterbacks is overrated but when a QB does it at the level of Cam Newton or above current Cam Newton like a Lamar Jackson, it should not be dismissed. It does change how receivers and tight ends are covered a bit and gets them more open.
That running ability makes it easier for other skill position players.
As for Newton's accuracy/processing. It is fair to say he is below average overall in those areas and probably always will be but with full season in New England he will be better. And Patriots coaches have already learned what he does well and what he doesn't do well and have made additions to the team to help out Cam Newton. I have confidence they will work out reasonably well.