This is definitely a concern, although how much of a concern it will ultimately be (in terms of the success of the platform) is not yet clear.
While we cannot yet determine how much of a concern it will be, it's nevertheless an issue. As in any community, a massive wealth gap is counterproductive, if not totally destructive.
From what I've read and heard in my 2 months here, it seems as if most whales are as focussed on building the network / platform as they are on earning Steem or Steem Power.
Of course, everyone wants to get rich, so even on Steemit, we may see an ongoing wealth gap. Instead of trying to stop the inevitable, maybe we should focus on ensuring the rising tide lifts many of the minnows' boats too. (An outcome that supply-side economics failed to deliver.)
That way, we can ensure that we have a long-term, viable platform that may not enrich everyone, but that does at least benefit everyone.
Essentially, that would mean that we have a meritocracy.