The Problem
Every post has some probability of going viral and getting a payout. Users have incentive to enter as many posts as possible to maximize the probability of one of their posts getting rewarded. Rate limiting to once every 5 minutes is too coarse grained.
The Desired Behavior
Users should be posting quality content and should be incentivised to post better content less frequently rather than poor content more frequently. We would like to achieve this without forcing everyone to wait hours or days between posts.
The Proposed Solution
Posting rewards should be reduced for people who post more frequently. Someone who posts once per day would get the maximum posting reward possible on their post. Someone who posts 2x per day would only get half the rewards on each post.
Someone who plans to post twice per day would need to be confident that on average they will make more than if they just posted once per day. This means that the average value of their two posts must be greater than half of their best post.
Those who consistently pump out quality content will still make more under this model regardless of their frequency. They will simply enjoy the benefit of less variance. Someone who pumps out spam and hopes to hit it big will see their "average quality" fall which means their big posts will pay them far less.
Preventing Sybil Attacks
The primary reason to post all posts under a single account is because of followers. Once people can build an audience it is easier for them to get votes. Someone who divides their posts among multiple accounts in an attempt to spam will not build an audience.
Users are still free to post every 5 minutes, but their profit potential will be dramatically reduced. By encouraging people to post less frequently, we are encouraging them to be more strategic on each post they make.