I think Lance will be the guy, and Purdy the backup. Purdy is basically Jimmy G+ to me, some upside, but not a ton. He played great this year, albeit he played a ton of lower level talent and was propped up by a great defense. Lance has the upside and at this point, you would think he's got to have that playbook down. Kyle Shanahan seems like the guy who wants to really see what he got in a player like Lance before moving on completely. If Trey plays a full season, I think he would put up some great stats in the system and get the Niners back to the playoffs again for sure. Big IF, I get it. Just my take.
As a 49er fan, I dont see how anyone can say they think Trey will be good or bad. We just havent seen enough of him to know, and I follow the team 24/7/365.
As far as Purdy, the main reason hes so good in the SF offense is because he processes things so quickly. Probably better than both Jimmy and Trey. That inlcudes reading defense and recognizing coverages pre-snap. On every play, Brock knows where everyone is supposed to be. So far, Trey hasnt shows he can do that yet, but hes gonna get his chance to show what hes got.
I really like Purdy and Im not so sure Trey would beat him in a camp QB competition. Fortunately for Trey, he wont have to beat Brock in camp, but I wouldnt be surprised if Brock is behind center come week 1 (assuming his surgery and recovery go as planned)