You raise a valid point. If the whales keep voting on their own content and keeping a tight lid on the rewards, eventually quality will drop off and they will be the last ones standing trying to dump their steem dollars for a fraction of today's price.
After getting dismal earnings on articles, many of them containing original photography, I decided to to spend more time on curation. I'm certainly not going to invest an hour into an article to make $2 or $3. Now I only write if I feel like it and don't really care if I earn anything or not. Steemit is still the best social networking site though in my opinion.