Yes, This happens with a lot of software products. You get a lot of mod developers who are in essence gatekeepers where you can't really get everything unless you buy more. And for the developers of the software they can't add these same features even if they would be great for everybody. They have to require people to go through the mod developers.
I don't believe it would be a copyright infringement to make a similar mod, And an additional level of protection would be if Someone makes the mod for themselves using AI And not making an exact duplicate, Or secondly if people make open source code that offers similar features but people work together and open repositories and also use AI code. An idea is not copyrighted but the code itself or the text and potentially even aspects of the interface could be copyrighted.
So in the case of making a modification that controls bots and helps to stop a forum from being overrun by them, there is plenty of knowledge out there about how to do that and we do not need to rely on the original mod developer to make that mod. The idea to make a mod that prevents bots from overrunning a forum is not copyrighted. And I'm sure a similar argument could be made for most every modification.