I think Brissett still has a lot to prove, in terms of mastering the playbook and making the kinds of throws and reads our system requires.
But I'm proud of the kid for what he's done so far, and you can tell Bill is proud of him too!
I love the guy, he is just so dang likable. However, as you point out he is still unproven.
Really someone like Ken should do this, but it seems to me that there are three factors to a successful quarterback:
1) Talent (throwing accuracy, arm strength, quick release, pocket awareness, ability to read defenses).
2) Intangibles (how hard he works, is he full of himself, does he listen to coaching, can he lead teammates, is he a "good person", is he smart, poise).
3) Organization/Luck (how good the coach and/or organization are, is the scheme match good, is he at the right place at the right time, can he avoid injury and be durable)
A few recent examples: Luck has talent and intangibles but is in a horrible organization; RGIII had talent but not intangibles, coaching, or durability. Brady had top talent, off the charts intangibles, and perhaps the best coaching/organization ever, and the result was the GOAT.
It seems to me that clearly Brissett has off the charts intangibles. Plus, he is in a top organization, so he checks two of the three boxes (if he avoids injury), so of course the Patriots love the guy. However, the talent is hard to judge at the rookie level, it is promising but as you say unproven. Looking at his college games, he is an elusive runner and absolutely strong as an ox (in several college games he shook off tacklers and prolonged the play like Roethlisberger). He has been very poised in college and with the Patriots. And, IMHO he clearly improved from 2014 until now, he seems to soak up good coaching.
....The question is probably his accuracy (a little unproven, although to his credit he didn't throw many interceptions in college) and perhaps the quickness of his release.
I am excited to see how he develops!