Going back to the "complete episode 1 to chat" suggestion, not only would that inconvenience those that don't care for the optional story, but the people running the bots would just implement a way for them to cheese through the story quests, most likely by using cheats to go out of bounds where enemies cannot touch them. They'll find a way to bypass nProtect GameGuard somehow.
All I can suggest is done personally is that a chat filter is implemented that's more dynamic than the one built into the client already and is done server-side. That way GMs can add words to the filter on-the-fly without requiring a client update.
From there, some sort of chat shadowban system can be implemented where if a bot hits too many words on the filter too often then their chat is hidden from all other players other than themselves. The problem with that though is that you need to ensure that real players don't trigger that filter too, and the bot owners will have methods to bypass the filter b changing the contents of their messages.
While it is true that they can bypass the anti cheat they can also bypass a chat filter too even if in real time. Completing Episode 1 would force a re tool of such bots but I understand maybe this is not the best way to solve the issue.