Yeah, I'm not really sure what this means in practice. I think you're being a little tongue in cheek here (or maybe I should say Heinlein was being), but I'm always very suspicious of quotes that sound cool but don't really say anything.

Women aren't superior to men. Men aren't superior to women. The very idea of group superiority is moronic. In fact, the reason why inequality always leads to problems is precisely because one person isn't superior to another.

When you say (or he says) "absolute equality" I presume you mean equality of outcome, or equity. This, indeed, is a disaster. It's why we have idiots like Kendi running around saying that any disparity between racial groups is evidence of racism. And trying to enforce it with his (Department of Antiracism)

Anyone who doesn't expect there to be differences between groups, isn't taking the concept of groups seriously. We could divide down any number of lines; race, height, age, sex, religion, and in each grouping we'd see differences. Trying to force there not to be is also moronic.

But equality, as in; you have access to the same opportunities as me. You have the same rights and protections as me. The set of "groups" that you're a member of doesn't make you superior or inferior to me or unfairly disadvantage you as you move through life. You are as free as anybody else to choose the direction of your life. I'd say a society built on any other ideal is inevitably going to fail or be forced to change. It's slow, but it's undeniable.