I've had similar thoughts, but the miner slot does provide some value such as anonymous account creation. I'm pretty sure Dan wants to keep it for diversification of block production, which is valid to me. But I don't agree that it should be paid equal to the backup slot.
Here's what the Steem whitepaper has to say about it, from page 22:
This process is designed to provide the best reliability while ensuring that everyone has the potential to participate in block production regardless of whether they are popular enough to get voted to the top. People have three options to overcome censorship by the top 19 elected witnesses: patiently wait in line with everyone else not in the top 19, purchase enough computational power to solve a proof of work faster than others, or purchase more SP to improve voting power. Generally speaking, applying censorship is a good way for elected witnesses to lose their job and therefore, it is unlikely to be a real problem on the Steem network.
But seriously, thanks for the real research and dedication to Steemit.