It can crank proof of work schemes to maximum, something like you need to burn 15-20 minutes 16 core cpu to post a single comment. It will be infuriating for users, but not cheap for bots

One solution is to get rid of anonymity online, enforce validation of identity. Every human only gets 1 account. And then we still ban people that use AI. Might take a bit but eventually we'll have filtered out all the grifters.

If that's worth the cost... probably not?