You're missing the value of NIL to Texas entirely. The bag man peddles raised funds from private donors. If that was also true of NIL, you'd have a case, but it's not. The value for Texas is a) legitimizing paying players and b) the incredible amount of opportunity to raise public money compared with the other 95% of schools. There will always be more money in NIL, regardless of school, than a bag man could offer.
If federal legislation ensures a fair playing field, the bag man is moot. Again, the bag man can not offer the same amount of money that NIL can. They can only pander to immediacy of the bag. While it's unlikely that the federal government will be able to create and pass meaningful NIL legislation, it would be a net benefit to regulate when athletes can first be paid, what ability states have to advocate for prospects to stay in state, etc.
There is significantly more value to Texas in setting a floor for how the big money works than trying to punish the small money.