The small SP holder also have some advantages. One of them is the fact that if you upvote them you know you'll have a bigger part of the 25% curation reward. Big SP holder can have very easily 10% of that curation reward for themselves, up to 99%.

Also when small SP holders are rewarded you know the distribution is more advantageous to you than if you only upvote those above you. So one must find the right balance. Sure the big SP holders are advantage but not to the extent that Steem doesn't make sense, on the contrary, you'll see Steem change the face of humanity for the very best and very fast for that matter.