I'll be honest, I've barely watched Lance play. I pulled this up to see what he had.
I just don't see it. At all. This guy looks like a late round 3rd stringer. Most of his "best plays" are runs. and the runs aren't even impressive. He has a loopy throwing motion that starts with the ball around his waist. His passes are not accurate. Even when he scrambles or on the RPO look when receivers are wide open, they often have to reach for the ball.
I'd almost guarantee this is Jerry's pick on the "we liked him in the draft" theory, not based on a single thing they saw in his NFL snaps. Contrast a prototypical size/speed type guy like this to the guy we know McCarthy liked, O'Connell, who is a non-athletic, accurate, traditional pocket passer.