I don't have any experience breeding dogs but my friend breeds Hamiltonstovares. I asked her about spaying/neutering dogs and she also agrees that you should allow a dog to finish growing before you spay/neuter. She says early spay/neutering can cause health issues. I think early spay/neuter is pushed by vets and rescues because of pet overpopulation. So many pets get loose and breed or you get those dumb parents that want to let their children "witness the miracle of life" by breeding their dogs. Then you get backyard breeders that say "I have a purebred dog. I'm going to breed it since its so cute and my friend has one of the opposite sex. We'll sell the babies for a few hundred". Vets and rescues want to help curb this and so they encourage early spay/neuter.
I have a problem with dog breeds that have health issues due to their looks. This is directed toward short-snouted dogs and other malformations that for some reason people think is cute. Breeds like this should be discouraged.