"If Joes Sports is selling balls and Joe's Sports B team is going to supplied ball worlds and Joe's Sports figures out which batch of balls is best they will be giving Joes Sports B team the good batch of balls. Why wouldn't they?"
You work for the people who decide what balls are legal and what are not. If you create a system where your major ball vendor/provider is doing things to cheat the system, maybe you need a better system? I'm going to point out that bats get used like this every week, based on their testing, and you have no issue with that. Here again, you are creating a strawman.
Everyone would send the best balls to their teams. Just like they do bats. Nothing is different. If the bats are ok because they have limits, so do the balls. Its the same logic. If it works for bats, it works for balls.
If nothing else this shows me just hot little confidence there is in the equipment testing.