I would expect that to have an effect, but if those changes cause him to go from looking like a really good QB to a below average QB, then I'd say he wasn't a really good QB to begin with. And when you watch his 2018 games you see his WRs and RBs bailed him out of a lot poor throws. He was also asked to make decisions based on his reading of the defense. That factors in as much as working with new players.
Again, I would expect it to have an effect, but I also thing his numbers looked better in 2018 than his skill level because of the type of offense that Utah State ran.