Practice is important, but guys being “gamers” is a real thing. Danny Wuerffel was a notoriously bad practice player. It drove Spurrier nuts. Urban Meyer didn’t like Chris Leak’s practice play, but Leak won him a championship in 06.
This works in reverse too. Feleipe Franks was the best practice QB perhaps in UF history. His practice play fooled two different coaching staffs, two OC’s, and was so impressive it caused a coach who has one helluva QB eye, Dan Mullen, to start him over a gem, Kyle Trask. But during games, although he had great games and great moments occasionally, Franks just folded sometimes, completely falling apart.
Just because Maurer or Shrout or Bailey aren’t looking as good as JG in practice, doesn’t mean they won’t outplay him in games if given equal opportunity.