He isn’t all that established. He started part of a season with mixed results that culminated in a really good bowl game against an ok opponent. He is only going to be a true sophomore as you pointed out. So it isn’t like a jr or Sr qb who has significant playing and practice time behind him, Zach is a young guy that started a few games.
So yes I do think it hurts him to miss spring and whether or not we will ever be able to establish exactly how much is of course impossible to say but if he starts slowly and has a couple of bad games early then I think we’ll be able to surmise it hurt him to some extent. If he has a mediocre season then we’ll also be able to say he could have benefitted from spring reps. He’s not a returning starter in the same way that an upperclassman would be and of course Zach only has one spring practice behind him as well. He needed this IMO although the situation is what it is so you just make the best of it and work on what you can.