Oh, so this is your rule. Cute.Cowboy’s Rule of Non-Macroevolution:
"All biological organisms have potentially unlimited genetic variation, restricted within their own defined species (on very rare occasion, genus) regardless of ancestry or time.”
Now show the mechanism that underlies your made up rule. The one that stops adaptation being open ended and continuous, and sets limits on the amount of variation allowed. I note that even within your "rule", you have contradicted yourself by claiming that potential genetic variation is unlimited, but restricted. Could you be any less logical?