Yes, an instructor is free to limit what is allowed in their classes, and should. A poor performing pistol takes up allot of time from teaching when an instructor has to stop range time to deal with a problem pistol.

Again, I've never heard of a range not allowing a hi point.

I'd be interested in getting a phone number for a few of these ranges so that I can call them and talk to them about this and see what they've experienced that led to that decision.
​​​​​​-Jake