Free downvotes alone wouldn't really inspire me, I'm not really interested to move rewards from Bob with his mediocre content to Alice with her mediocre at least.
(And Alice might be Bobs girlfriend btw)
If on the other hand the downvoted rewards would be not just returned to the pool, but actually burned, that would be another story.
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I agree with you that burning the downvotes reward would have been good incentive to downvote if it had been like that from a while ago. But today that would be too little too late.
Your Alice and Bob example assume both content are equally mediocre, in reality one has to be less mediocre and therefore of higher quality. It's a step in the right direction.
Since the financial incentives are the reasons for whales to vote and bidbot use, quality of content is irrelevant. Profiteers don't care.