> Just put in a super basic arbitration process that is costly to game for "non-real" people

I think your "just" is hand-waving away a lot of complexity. A person deployed these bots, and if a bot account gets put into an arbitration process, that person can go through the process themselves to pass the arbitration, then set the bot running again.

> that person can go through the process themselves to pass the arbitration, then set the bot running again.

That is not scalable, which is exactly the point.

It's far more scalable than the arbitration process itself. Arbitration will never win such an arms race.