High schools have been slower to change than the NCAA. The NCAA completely revamped weight cutting in the late 90's after three wrestlers died of dehydration in one year.
But some states, like Iowa, have more stringent rules. I think they call their test a body composition assessment. Boys can only wrestle at the weight they would have if they were properly hydrated at 7% body fat.
I agree with you that it'd be better if fighters didn't cut large amounts of weight. But that's obviously not the case. And until it is, I think the current system is better than same day weigh ins. Many fighters will still cut massive weight for a same day weigh in, then they'll fight with a severe increased likelihood of brain damage.
A better system than either of them would be regulation to determine what their hydrated weight would be at a certain low body fat percentage and limiting them to only fighting in that weight class or above.
I think that would be a good system, but having them weigh in right before they go into the cage or an hour before would severely discourage weight cuts. I think the max you would see would be ten pounds.
In fact, if you had them weigh-in just before they entered the cage and they had to do the whole walkout and everything and the fight would be cancelled if they didn't make weight, then we likely wouldn't see a fighter miss weight again and they likely would be cutting no weight at all.
The system your proposing is definitively more of a scientific approach, but it has problem associated with it. Ex) There are large differences in skeletal density which results in some people having heavier bones.
Also if the body fat percentage is a low standard that every fighter is compared to, then some fighters will be at an advantage if they have a lower body fat percentage than the standard and fighters with a higher body fat percentages will be at a disadvantage.
In a way it's like genetic profiling for a champion. Fighters with a very low body fat percentage are going to have a unfair advantage in my opinion.
Additionally, this approach will really result in a cookie cutter approach to each weight class. Typically there is a certain range for height and weight for a fighter in each division, but this approach would get rid of all the outliers in each division.
If I'm interpreting this wrong, let me know Smacky.