There is bots everywhere, it has nothing to do with the platform, it has to do with attackers having an incentive to do mass account farming, no platform is secure against it.

With banning and deboosting they need to be very accurate but with filtering they can be more liberal in excluding

Super easy, just make a web-of-trust type of thing: messages are only visible to those who already vouched for you. Otherwise, you pay $0.01/per message/per user reached.

not really. there are easy heuristics to filter out bots with good confidence. FWIW i don't see any bots posting anything in my feed

Yes your individual feed isn't really relevant if we talk about the masses, Reddit accounts are for sale quite cheap, HN as well, X too and so-on, it's literally just a matter of means/methodology. If I want today to do 1000 random posts talking about a certain thing, I could.

my individual feed does matter because it shows that it is possible to curate something without bots which is obviously what XAI would do