It's one of those things where you can't win a discussion.
If we say "he should have put Trezeguet on for Traore at 60mins" when we are 0-0 with the opposition attacking, we just don't know if that's the right call.
Maybe we lose the game. Maybe we win it. Maybe we concede 7 goals after Smith makes a sub we want him to make. Maybe Grealish makes a run he wouldn't have done with Traore on the pitch and pulls a muscle and is out for a month.
Smith sees the players on the training ground and has several tactics ready at any time.
So yes, we can have a discussion and have opinions, but they are happening in a parallel hypothesis universe so are mainly pointless.