My point is whether you use that or any other method to determine a budget, a lab-grown stone at that price will be objectively superior to a mined naturally occurring one at the same.

Or the cheeky version: use such a rule to determine the clarity, colour, etc. of natural diamond you want; then buy that lab-grown and pocket the difference.

I agree with you. My point is that logic clearly isn’t playing a role anyways. The origin of the stone, even if it’s fungible or even superior, likely has value to these people.