I never played quarterback outside of rec league football on Long Field, where I was pretty darn good! That said, I have always suspected that one difference between good quarterbacks and not-so-good quarterbacks is their ability to anticipate and throw to a route instead of to an open man. This involves knowing your receivers and also being able to read the defense in order to, in a sense, predict where the openings are going to be.
When you watch a really good quarterback, you can see them throw the ball to a region on the field before there is even an open receiver. That may be a crossing route in the middle or a back shoulder throw along the boundary, or even just a long bomb. But your worse quarterbacks seem to only be able to throw the ball to a receiver that they can see is open. I feel like NU has had a lot of QBs like the latter. They need to see our guy beat the coverage before they feel comfortable throwing it.
To me, it seems like Ben Bryant does as good a job as anyone at NU in a long time at throwing the receiver open, whereas Sullivan looked afraid to let go of the ball all day. He only threw it if he saw space between the receiver and the coverage. To be honest, I always thought Clayton Thorsen had this problem a little bit too and it's what kept him from becoming a truly great NU quarterback. I would have thought that with a four year starter with his physical skills, we would have been a pass happy team that could really move the ball, but he never seemed to take that step developmentally.
I'd be curious to hear from others who know the game better than me if I'm correct in my thinking or way off base.