Or, we could just avoid the problem as much as possible by not willingly opening things up for abuse. If users want to post more than four times, they can do that. They just won't earn as much. And chances are, if they're posting more than four times per day, the quality of their posts probably won't be that great anyway and probably won't be deserving of large payouts.
The four post limit/penalty doesn't seem to be a big deal in need of a "fix."
It has the psychological impact of discouraging engagement and adds unnecessary complexity to a system.
I don't think it discourages engagement. It discourages abuse - in the form of sock puppets and spamming. This is anecdotal, but I haven't seen many complaints from users who think that this needs to be removed. The limit doesn't mean that a user cannot earn - it only limits how much can be earned after a certain number of posts. With a stake-weighted system that can be and has been abused, I don't believe the limit is an actual problem.
You're right. We may ask this first; how many articles/posts does a professional writers create per day?
Not all posts are going to be (nor should be) professional writers. Approaching it from that angle impairs the growth potential of the system to reach a much larger audience from the start. There are many different use cases for this blockchain, professional writers being only one of them.