How do you figure? A currency no central authority has a monopoly on deciding supply is on it's face more decentralized, and an improvement on the social front, regardless who has what.
A currency entirely owned by one person isn't a currency, and people actually using it causes dispersal to a naturally occurring Pareto distribution over time.
Currency’s is not wealth , most wealth is not stored as a currency or cash [1] it is stored in assets.
If you see how actual physical cash [2] i.e. dollar bills ownership then it won’t be distributed in a typical Pareto curve.
If I don’t have access to notes and coins. I won’t use them so government makes sure I have access . They still will mint it even a at loss like the penny.
Also all power distributions are not Pareto distributions, bitcoin is lot steeper than the standard ones used in economics , that is what this article implies /shows in its analysis .
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[1] including other cash equivalents like bank accounts not just literal printed money. Accounting standards has well understood definition of cash equivalents
[2] comparing against only physical cash (M0) because there is finite fixed amount of bitcoins available at any given point It is not possible to increase bitcoin M1/M2 supply like with fractional reserve banking so you cannot compare against narrow money let alone broad money(M3/M4)
A negative interest rate decentralises money because your balance no longer grows automatically through interest and capital gains just because you have a lot of money, which is a self reinforcing feedback loop that concentrates ever more money at the top. If you want money, you are going to have to earn it yourself instead of letting others earn it on your behalf.
Of course, once you have solved the money question you notice that it is not just money that needs to be decentralised. Everything else, housing and the land it sits on must be decentralised. CO2 emission rights must be decentralised. Resource extraction rights must be decentralised. Intellectual property must be fixed. Taxes must be decentralised. Income earning/education opportunities must be decentralised.
It is kind of funny how solving all these challenges would get you to something one could call true anarchism, yet actual anarchist movements aren't even anywhere close to solving them or consider them important enough to solve. They just change the governance model and assume that the aforementioned problems will resolve themselves once people get to organize their society in this way.
All of this would bring us closer to a free(as in freedom) market. As it stands right now, most capitalists are happy calling this broken mess a free market. You're free to choose to not be allowed to legally exist. The truth is that it is a free market as in free of cost as there are so many tax loopholes to be exploited.
In the bitcoin world ownership is lot more concentrated than in the real world, which makes truly decentralizing anything else hard if not impossible.