Interestingly you can believe that hierarchy is natural and still be a leftist, because coercive hierarchies (such as capitalist or the state) that the left is against prevent these natural hierarchies from emerging. The problem with the right is that they have a model of society in their mind and think that any divergence isn’t natural and must be fixed (by either capitalism or the state). While the left understands that there is no reason some people can’t be in power and so want’s to equalize the playing field.

Human beings aren’t made equally and there will always be some hierarchy in human society. Leftists just want to give everyone the opportunity to rise up the ranks instead of just the “right” people. That is why everyone must be treated equally you don’t know where they exist in the hierarchy.

Technically there isn’t a single social hierarchy. But multiple overlapping ones. Some people are better in some things and other are better in other things. Saying that everyone is equal is too simplified. Society is more complex than that.

But as a generalization (especially when compared to the right) it is correct.