Success in wrestling doesnt guarantee a succesful transition into mma . Its a bonus but there are more deciding factors. The difference in wrestling is not about freestyle being better or worse. One could also argue folk is better because of ground control (very important aspect) Most high level wrestlers can adapt in a short amount of time to other styles because they have learned to shoulder a very high training load, are mentally strong and have high level motoric abilities. The equilibrium of most wrestlers is simply outstanding no matter which style.
Its about talent pool size very simple.
Folkstyle only being used in the US has a much smaller talent pool and because of that less elite talent (they still have elite talent!). Iron sharpens Iron. If you make it in freestyle you have proven yourself against a shark tank of the best wrestlers from all over the world, Russia, Iran, Japan, some west european , turkey., Cuba....etc. And they have national support programms.
I am a little curious how a wrestling coach doesnt see this.