There's value for a player going into a game knowing they'll be the starter. That's what happened with Dart. His preparation the week before was knowing he'd be playing, running with the 1's, etc. In the small sampling we've seen of Connover, he came in mid-game for an injury. Wasn't he also running the scout team offense this year? That means he was likely practicing the plays of the opposing team more than he was his own team's. If he didn't seem in-rhythm, maybe it's because he never had the time to develop it with his receivers, not that he's not capable of doing it. Rhythm, timing, cohesion as a unit - those things take reps, time and repetition to develop. Dart had at least a week to do this. Conover, not so much.
Also take into consideration the defensive scheme dart was playing against - it's designed to allow giving up yards.
I think the frequent expressions of Jacob's "lack of progress" are basing far too much on too little of an abnormal sample. What have the coaches seen from him every day?
He'll be just fine.