This is an oversimplification (sometimes simple math really is too simple).
Winning and losing makes all the difference. A stud player isn't going to turn down a $1 million deal from a USC program that's competing for championships because they could make an extra $150k from the collective in Athens or Gainesville. A five star player on a great team in LA has access to branding and networking opportunities that are tough to beat elsewhere. We benefit from this effect at Miami!
You’re underestimating the tax burden. It would be between 42-48%. A 1 mil NIL take home is closer to 520k, and they aren’t currently winners where players would take a discount. I think it’s naive to believe kids would pass up several hundred thousand to play for a mid program.