While at the same time the power is in the hands of a relative few, those with the most power also have the most to lose if the system fails. They also have the most to gain if the system succeeds.
The fact that people can buy Steem Power, I don't see as a problem, I see it as a feature. In fact, when someone buys Steem Power, they are benefiting everyone else involved in the Steem ecosystem, because they are the ones who are attributing value to the token. Without people buying Steem, Steem the token ceases to have value in the real world, and what you end up with is a Reddit where you can earn worthless digital tokens.