It's not easy to optimize the quality and rewards and the whole Steemit system.
The @complexring reply already shows how your solution may become ineffective, but there are other issues: lower rewards to established authors may bring them out of the platform or make them publish less contents (or lower quality ones). Note that I'm a minnow too, so not defending established authors for some personal interest.
It's a complex balance and there's not quick and easy solution IMHO.
He and jesta are worried about Sybil attacks. Nothing stops a Sybil attack at the current 25% rate, right?
Lower rewards to established authors would mean that they have to post less, yes. And that's a good thing - would you rather have several people with several interests and everyone else working for free, or rather more authors and more diverse content, and more people receiving money for their work? It's all about a sightly better reward distribution and people actually reading the articles vs. mindless upvoting of established authors, because their articles pay out.
Also, being limited to posting less times a day, means that you will push for higher quality articles.