True, this initial distribution of Bitcoin isn't desirable longterm.
The important question is: do the fundamental dynamics of the system lead to a less unequal distribution or to even more concentration in the longterm? I'd say the longterm dynamics of a system that's capable of reaching some equilibrium are hugely more important than its initial state.
Every time, some Bitcoin whale buys something with their coins, they're very likely flattening the distribution. Since Bitcoin doesn't earn any interest, whales cannot just spend the earnings and keep a constant balance. Every time (almost) they spend, the distribution becomes more flat.
As long as the Bitcoin price were to rise, the incentive to buy something else with it would also increase. Combined with people having finite lifespan this will probably lead to most whales spending sooner or later.