That's a good point. People look for absolutes. If I use hardware cloth I will absolutely never have a predator problem. If I buy a certain breed the pullets will absolutely start to lay at a certain age. Real life doesn't work that way with living animal and here you have the living chickens and the living protozoa that causes the cocci problems. A double whammy.
I don't look for absolutes, I look for ways that improve my odds of success. I believe that introducing my chicks to the environment they will be exposed to as soon as possible (feeding them dirt) will strengthen their immune system and enable them to better handle what they will eventually face. And since cocci thrives in a wet brooder, coop, or run or in dirty water keeping their water clean and their living area reasonably dry greatly improve my odds of having healthy chicks and eventually chickens. That doesn't mean I will never have a cocci problem, but I do thing it tremendously helps my odds.