Well, yes, and to go further, most of the famous philosophers had things to say about justice, and so do most religions. (So why single out Marxism and and Postmodernism?)
Do any of them say "power laws, what can you do?" That seems like confusing what is and what ought to be.
Only because they're some of the most recent philosophies that have had a very widespread impact and also due to them emphasizing Collectivism as opposed to Individualism. Postmodernism is born out of Marxism and Marxism pushes the equality theme hence fairness. I'd say that's a fairly valid reason to cite them?
Matthew 13:12 "For whosoever hath, to him shall be given, and he shall have more abundance: but whosoever hath not, from him shall be taken away even that he hath."
One could take that to be in reference to the general dynamics of power laws.
But, to reiterate my actual point, you find the same behavior related to 'fairness' in the animal kingdom, so it's not a uniquely human thing. That also makes Marx and Postmodernism irrelevant. They're almost a natural consequence that arises from some deeper, pre-existing thing.
The Is-Ought problem is relevant. If we accept that the distribution of power in society and the distribution of individual contribution follow power laws (they certainly seem to) then in response to "what is" as a society we have to make a decision about "what ought to be" in terms of how we run our society. You have to make that choice but the David Hume points out with his Is-Ought problem that you cannot link the morality of what you think "ought to be" with what is.
This means that whether Marx is saying well it seems that Capitalism has some problems that eventually result in it eating itself with all this power and wealth going to the top, the middle being stripped out and the rest winding up dirt poor on the bottom, so we "ought" not to do things that way OR You say something along the lines of supporting the current capatilist paradigm, you can't compute whether or not you are making the "right" choice from a moral standpoint in either case.
My line of thinking for what "ought" to be is that if nature really does seem hell bent on organizing things a certain way, how likely is it we can do anything about that? And if going against the grain seems to produce perverse results without much benefit, than why not just go with the grain and take the good with the bad?
Going against the natural way of things is what I'd call civilization. Giving up on this is sort like saying that justice is an awful lot of work, so why bother with having police and a court system? This would be unpopular even with libertarians.
But in the end, this is all about costs versus benefit, which deserves more than a one-bit answer. There are many possible civilizations.
If you think my position is the nihilistic option of "we can't do anything,so let's throw the whole thing out" then you have gravely misunderstood.
My point isn't about the cost/benefit analysis. It's about finding and understanding the boundary conditions of the system and not trying to get to some delusional Utopia.
I'll state it another way. Freedom of Speech. Widely considered a good thing. Except for those who don't like what you're saying and want to shut you down.
Ok, so we have a lever that we can slide to different settings. Either, you're allowed to say absolutely anything with zero restrictions, or you're not allowed to criticize the regime in the slightest or the lever is set somewhere in between. The question is "where is the optimal place to set the lever?". It seems setting it to North Korean setting where everything is completely restricted doesn't produce good results. Ok, so we set it in the other direction? You can say anything. This seems to be much better. Except it has this consequence that since people can say anything they can say ridiculous things that you wish they wouldn't. And you just have to accept that. There isn't a setting where you can say whatever you like and so can everyone else and no one ever says anything you wish they wouldn't. That setting doesn't exist. This leaves you with the reality of "there's always a small amount of shittiness even in the optimal system."
That's what I mean when I say you have to go with the grain and take the good with the bad. It means learning to live with the parts you don't like, not pretending they don't exist or advocating for the levers to get set to some impossible, magical Utopia setting that isn't commensurate with reality on a fundamental level.
Do any of them say "power laws, what can you do?" That seems like confusing what is and what ought to be.