So (with one exception), at the upper tiers of stakeholders, we basically have a proof-of-stake blockchain masquerading as a social media platform.

Yes. It crowds out genuine effort. At the top end you have a purely inflationary high-APR DeFi chain that wants plausible deniability. And at the bottom end it's easier to churn out spam or plagiarized posts than it is to write genuinely good content (which has a high chance of getting lost in the shuffle anyway).

We've talked about the self-vote phenomenon before, and that aspect doesn't really trouble me. I only see over-valued and under-valued.

I think that it's a useful rule of thumb to assume that people aren't reliably good at evaluating the quality of their creative output. And humans are better at understanding bright-line rules than at making difficult judgments like what a post is worth, so I think it would be a beneficial norm to have even if it isn't 100% of the solution. I could also be on board with a norm like putting a rewards cap on posts that get auto-voted on (I think there can be good arguments for things like UBI, but it doesn't make sense for people to be making as much as the big accounts are making with upvu posts).

Campaigns against self-voting (IMO) will just spur the creation of Sybil accounts.

Sure, there's no single perfect solution. I just think the chain would work better if it had some more robust norms than "whatever big accounts can get away with".