There is some truth in what you say. The way I see it though is that steem is a unique community project and the fact that it is licensed protected means all the brain power from devs all over the world will come to steemit, this to me is powerful. The fact that everyone contribute for the betterment of the same platform. Imagine what bitcoin would be if all the altcoins devs were contributing to bitcoin only..
I have often expressed my disagreement with building hundreds of different app based on the steem blockchain for the same reasons I've just mentionned. If all these people would work on the same project that project would have higher chances of making it big than all the other 100 combined. This is why I was really excited by the busy announcement, because they are going to allow these apps to be integrated within the same site, this is huge for both busy and the apps developers. When people work isolated in their corner their lower their chances of being successfull, why do you think companies create partnership with each other ? This is particularly true for social media sites which are very difficult to bootstrap into mainstream nowadays.
Yes sybil attacks are a real problem. The day we find a way to solve proof of unique individual we are going to solve many many issue, not just in steem. The problems of power concentration/distribution could be solve though, maybe by using outside parameters that are not in the blockchain, such as reputation, points, etc..in order to create a voting power score that isn't just based on how much money you have.