I don't think anyone rational expects him to be more than a transitional QB that can still put us into a position to compete while the search for the next starter continues. Of course it all comes down to the question whether the Pats and Cam will find common ground on the value of the extension. But if they can, then he is an absolutely fine option to run the team through this transition.
He has his own specific strengths and weaknesses as every other QB but unlike most due to difficult circumstances this year had to learn most about the offense on the fly.
I disagree that there are not still 1-2 corners for him to turn. Obviously he will never run the offense as efficiently as Brady did but if that is anyone's expectation they might as well turn the tv off because they are dumbasses. At the same time if he gets to spend an entire offseason with input from McDaniels and BB I am pretty positive about him improving in multiple areas e.g. presnap reads, pressure and pocket movement. It won't be revolutionary but even a 10-20% improvement would go a long way.
Either way, we will know one way or the other what people on the inside think in March.