The solution is very simple: Stop ALL US citizens from sponsoring their parents for US permanent residency.

In other words: Eliminate the category in the Family-Based immigration system that allows US citizens to sponsor their parents for green cards.

ALL US citizens should be allowed to sponsor their parents for a multiple-entry visa which will never become US permanent residency. Then, all US citizens would be equal. No unfairness any more.

This is exactly what Canada is doing. They have eliminated parents sponsorship for permanent residency in their immigration system. Instead, Canada allows the sponsoring of a 10-year multiple-entry visa for parents of Canadian citizens. That way, families will not be separated.