[__MatrixMan__]

I think the bigger problem with #3 is not that nobody buys the equality claim, but that we accept the premise.

If all humans were equal, there would be only one human. That's how equality works

The underlying claim is actually that all humans are of equal value. Yet there's no clear way to map humanity onto the number line. No generally accepted evaluation function. Egalitarianism declares such a function and then leaves it lying around for oppressors to define.

This makes us weak against attacks where we're pitted against each other under the oversight of some master and we accept the deal because it makes our type of people more valuable than some boogeyman-type of person. This works because once we accept that there is an evaluation function, as you say, nobody buys that it maps us all to the same point.