2. Reading defenses pre-snap
This really has nothing to do with Justin Herbert in particular and is more indicative of the problems that every rookie quarterback faces when they get into the league. The NFL moves much faster than college football and the defenses you face at the professional level are far more complex than those you face in college.
Every rookie quarterback has some sort of learning curve that they have to endure when they take the step up to the NFL and Herbert was no different. That is what makes his performance in 2020 so special.
Those that are cold on Herbert point out the fact that his numbers were not as good against no pressure last season compared to when he was pressured. A big reason for this was due to the fact that any time he was not pressured he was delivering the ball almost instantly (because he was always pressured). This would often result in a pre-snap read and bad play design in which the first option did not get open off the line of scrimmage as intended.
That will hopefully improve with better coaching but it will also improve as Herbert gets better at reading defenses. That will allow him to make adjustments at the line of scrimmage and while he might not be on Philip Rivers’ level in year two, he definitely should have more freedom to do so than he did in his rookie year.
Patrick Mahomes infamously said that he did not understand how to fully read an NFL defense until his second year as a starter. The same is likely true for Justin Herbert.