If Cam can't play any better than he did last season, then he shouldn't start, but he looked better to me so far this preseason, especially last night vs. Philly. I know, Philly didn't play all their defensive starters but I saw a difference in him as compared to last season. To me, Cam looked like he had a sore arm last season. Last night, the throwing motion looked more natural, more athletic.
He also looked more comfortable with decision-making and processing. He seemed to be getting the ball where it needed to be, in the rhythm of the play progressions. The Pats have a complicated system. Maybe Cam understands it better now. Cam is probably at his best if he is going on feel or reaction vs. having to think about everything.
I am hopeful that Cam will play well enough to be the starter. I think that is better for the Pats and for Mac Jones.