The principle is not and has never been "try out everyone on the roster in a live game to determine who's better" as that's a) impractical and b) unnecessary for a lot of football positions. Again, that's because the only positions on the field that never sub out are almost always the QB and most of the time the offensive line. In other words, you have game tape of players 2 - 3 deep on the chart for all but a few positions every team, every year. You never addressed the point of why a coach would change the primary defender on specific receivers in the middle of the game, or you can't address the entire concept of sub packages for situational football because your view point is simply this, "Coach says best practice = starter = best player." However, we all know that good coaches constantly review game tape, especially the game tapes of ones that they think is significantly underperforming expectations. I say significant because we're not talking about Milton being able to produce on a level like Hooker did, but the discussion is about if he's even a starting QB in the SEC. If someone is underperforming that badly, do you think the coach should care how said player performs in practice? It's like designating an NBA player as your shooter because he can hit 100s of 3s in a row during practice, but he only hits the basket at a 28% clip in the actual games.
If I could get Heupel in a room alone for questions, then the first I would ask him is if he really thinks Milton is doing well enough to be competitive with other good teams. I'd be willing to bet my house on him thinking that Milton isn't good enough. Why? I refuse to believe that a coach with the resume you keep referring to concludes that Milton is an "adequate" QB. That would then lead me to ask, "So you foresee Nico playing below that level if you put him in a live game situation?" If he says yes, then that's frightening to me for next year. He implies we have a QB that was ranked number 2 in the nation that can't understand the simple offense he has constructed for Milton.... even with Nico being enrolled and with the team for like 10 months now? That's the only explanation that I can come up with personally, and that's not good news for anyone here.