because he's a bit too OP. the entire civ shouldn't revolve around one hero.
Balance changes' should not worry about whether AI can use the changes or not, and besides, using your own argument, "it's just one unit you're never gonna make again" what's the harm?
I'm here suggesting things I see fit for more varied and balanced multiplayer games,since that's what actually decides meta in most games. sure,there are bigger problems plaguing it for years, but why should that stop us from making better balance. no offense but this just sounds stupid to me