i dont get the problem with reloads
I think the problem may be the instructor's perception that faulty ammo may delay the pace of the class, with too much time spent helping one or two students to stay with the program if their ammo is problematical.
That said, I have certainly used my own reloads when I've been the student, and have no issue with it with my own students. Ammo is just too scarce and expensive now, and can easily exceed the cost of tuition.
Rimfire guns certainly have a place in defensive training.
I am organizing a defensive carbine class, and will probably allow .22 conversion units or dedicated .22LR uppers for most of the class, the exception being malfunction drills, which will require the centerfire guns.
My opinion is that there really is not a meaningful difference between .22LR recoil and .223/5.56mm in a carbine, and training for longer ranges is not a factor since a defensive shooting beyond 15-25 yards would probably be very hard to legally justify. Longer range training (beyond 25 yards/meters) serves best a a confidence builder.
In contrast, .22LR in a defensive handgun class will not serve the student quite so well as a conversion unit in a carbine, since the rimfire handgun lacks recoil management. (This is one reason why I have a preference for the Colt conversion unit for 1911s, as it does have at least some recoil due to the floating chamber). Still, for clearing a concealing garment and delivering the first shot against time pressure the service-style .22 handgun will serve.