In some sense i'm assuming wealth is a pref-A phenomenon, yes; not that "capitalism makes it so". There need be no formal argument here: all research into all wealth distributions in history are power-law; and a vast array of social phenomena are pref-A. And pref-A produces power-law.
As an empirical matter, the burden of proof lies with those who say "there is some other process" to show it. Since the PA process is demonstrated without exception.
Formally, why should we expect wealth to be a PA process?
Well, formal arguments will always be toy and disappointing, but get someway to explaining what's observed empirically. But:
Economic transactions are, roughly, exchanges of time. We have a fixed quantity of time each, and Alice offers some time to Bob, who offers some time to Eve... and so on.
Wealth is your net ability to draw down on the time of others, as a function of time. By spending X amount, I can obtain Y time from P people.
Assume, at t=0, everyone has an equal ability to draw down on the time of others, and an equal preference for exchanging their time (1hr for whatever it takes me to do, for 1 hr of whatever it takes you to do...).
Now, since we have different rates of production and produce different things it becomes wasteful for me to spend 1hr for your 1hr when you dont make what i want; or someone else makes more of it faster.
Our desire not to expend our own time needlessly, to waste our finite quantity of it, means we allocate it to where the ratio from ours/others is most efficient.
That is to those who can draw down on the time of others most, we give some of our own; and to those who can the least, we give none. (To, roughly, quote Matthew).
Simply in the pursuit of not having our 100 years wasted egregiously. And there are many compounding effects, not least this. For as soon as any inequality enters those who then have more can do more, and so become ever more effective at what they do.
We will not work a month to buy a t-shirt when a t-shirt can be made in a factory for a minute of our time. It makes no difference that the factory is owned big Capital (omg!">?!?). And if we were to that, there could be no "factories" of this kind -- since allocating resouces according to what minises wasting our time gives us more time, without which we cannot develop anything new.
All this is somewhat irrelevant however. As above, the burden is on those who say something else is conceivable to show (1) what their conception is; and (2) it is physically possible.
If all alternatives amount to global coordinaton across the species such that we are each programmed Marxists acting like drones -- or, likewise, non-agression libertarians -- you're then talking about a different species.
Wealth amongst the bees might be a little more normally distributed, for sure.