I think part of the problem is trying to make rules that are measurable that will stop puppy mills but leave other breeders alone. I think a quota on how many breeding bitches they can have on one property might help. Eg set the limit at something easy that no working dog breeder would have. Or where it gets to be "farming" ie the dogs are not getting enough human contact because there are so many hours in a day and not enough to spend any quality time with any dog. And cleaning the cage doesn't really count.
Personally I think 10 bitches is too many and 30 is ridiculous so 300 (Yes this exists in Victoria) is a puppy mill and should be shut down. You can manage 300 sheep but 300 breeding bitches is wrong - in my opinion. And something else that would be easy to measure is the ratio of full time staff or staff hours to bitches.
A puppy mill with 300 bitches - is going to overwork their boys too - hence the age restriction there. An Adelaide based poodle breeder found out one of her males had been taken by a puppy farm. It was kept in a tiny cage where it couldn't properly stand up and turn around, and only got out for breeding duty. That's the kind of thing that should be outlawed. The ANKC poodle breeder (has really nice dogs), got her poodle boy back and rehomed him in a much better environment.