I think a flaw in your argument is that you are speculating about the future of bitcoin, but applying the current day bitcoin wealth distribution. As if as we go from here to sole reserve currency, it won't change dramatically.
First attempt to prove that after bitcoins grow to the point of being sole reserve currency half the bitcoins ever created will still be in their current owners hands. I think it's possible that there would be enough distribution of coins along the path that at the end of the road the concentration aren't in higher ratios than with our current system.
I think that is being extremely optimistic, but even if your scenario were to prove true-- nothing in the world would change at all, so what would the point of the currency be? Maybe I'm asking too much, but in other words-- what would be so revolutionary about it?
I don't think anybody should have any delusions that bitcoin "solves" disparities in wealth. There will always be wealth disparities, that is just a reality. If the only value bitcoin was touted to bring to the world was no more wealth disparity than your point is valid and bitcoin will be pointless.
The world can change dramatically and still have rich and poor people, not sure why you would think otherwise.
If anything I think bitcoin can bring somewhat reduced unfairness in wealth distribution long term. Sure there will be some wealth concentrations around the smart and business saavy, around the ruthless and psychopathic, and around some due to early adoption for awhile. However this is true with our current system, and with bitcoin you get the benefit of not allowing the rich and powerful to crony up to the money printers and get first dibs like you see with most fiat.
So my prediction would be somewhat more fair wealth distribution, as well as all the other advatages that comes with sound AND programmable money. Sounds pretty good to me.
Edit: My personal belief is that current wealth distribution is not 100% "fair" but that neither is !00% uniform distribution of wealth.