Since there's nobody in the Black Legion that could take over, i'd nominate Huron Blackheart to take over. He's interesting enough to be a main guy, plus he has a good amount of in-universe power to pose a challenge at least. >>63823677
ADB posts things like this on Reddit all the time. I remember he wrote a exchange like this with Abaddon shit talking Gulliman, when he got called out by another user, that guy was downvoted into oblivion. >>63823715
I don't think you quite understand why I call Abaddon a mary sue. According to Black Library canon (aka ADB) he has full power of himself and isn't a slave to the Gods.