Well the problem is that those who hold most SP get huge gains for every action or inaction compared to everyone else. As an example @pfunk is getting around 1 Steem Power per each upvote! (source: https://steemdb.com/@pfunk/curation). I'm almost a dolphin myself and am getting around 0.03 SP per mine.

So just by taking into account curation, the wealth will slowly trickle up. Then you add the inflation, big rewards for voting on own posts and you end up with this trend that we have now.

To add to this, whales are starting to sell their votes! Instead of figuring out a way to reward good content, they just sell it to anyone who wishes to throw money at them.
The rest of their voting power will probably go towards close inner circle, too much of money to pass by.

And final issue, since wallets of whales keep growing at increasing rate compared to everyone else, they can keep powering down every once in a while and still stay ahead of everyone else.

Most of these big wallets were acquired in the "instamining" phase when the site itself was not out yet. If the distribution would had been fair, Steemit would look a lot different and it would had been adopted by the rest of cryptousers, now it is struggling to do so.

I might be wrong and I hope so, I really do - but the very bad distribution is a issue that will keep Steemit in its shadow for a long time. Even if Steem fails, due to these issues, someone will copy the idea and make it work and for that I'm glad.

And how to fix this issue?

Burn all the Steem earned in the early mining phase or majority of it. Voilà. This is just a rough idea I saw suggested by someone else, I'm sure people could come up with far more sophisticated ones. Of course the whales wouldn't like it...

But it speaks volumes that I'm still here, and I will continue to do so until something better comes along - maybe that never happens? It's up to us all.