When you place a tangible value on trust, trust becomes a commodity to be bought and sold. See:

1. Old domain names bought solely for their old SEO rank.

2. Apps on mobile app stores are sold, and updates begin to include shady privacy-invading malware.

3. Old free software projects on various registries (npm etc.) are sold, with the same result as (2).

Agreed, being able to become part of any group makes this problematic. Without repercussions, it seems difficult. Detection of ownership and the following loss of trust seems to be also in order. Or make the trust innate, not sellable to others, under the assumption that you cannot sell yourself.

Otherwise, it seems really like a cat and mouse game. Another option may be to force SEO to be indistinguishable from the best content. Is that the current goal?

Yes, but it feels like an approach that would not allow you to do anon searches. I guess pseud searches may be good enough.

I suspect this is actually one of those fundamentally hard problems.