the last few weeks of transactions when we apply the rules of the first two parts of the EIP to it, don't seem to actually support the narrative.

I assume you have a link to this? And it studies post payout distribution under the new curves? Note that this isn't enough to demonstrate effectiveness (or lack thereof), because incentives will be shifted significantly and change the distribution of posts and claims.

Concerning the split stake: splitting stake is as neutral under EIP as linear. If you are saying that the curve is a direct measure of influence, this is not correct because the reward curve is applied on top of the total rshares of a post, not to each individual vote (forgive me if you already knew that, but this is not obvious). Meaning, 10 votes of 10 rshares does the same to a post as 1 vote of 100 rshares.

I have to admit I do not understand your curator author bucket split. Will probably need some examples on how it works.