Karthus is not strong because of Dark Harvest, he is strong because he is now able to take precision secondary which works extremely well with his kit.
Reverting Dark Harvest would still leave Karthus at an absurdly high winrate as he performs almost as well with Aery as he does with Dark Harvest.
As long as Karthus is allowed to take Presence of Mind + Coup De Grace / Last Stand, nothing will change and he'll still be banned almost every game in high elo.
Karthus isn't the problem, note how his winrate has jumped almost exclusively because of this patch. He gains too much damage from Dark Harvest alone, and given that he's a pretty spammy champ with tons of teamfight presence, he's going to make the most use out of it. That's why he's so strong and you're seeing APC Karthus everywhere.
Dark Harvest needs to be changed or nerfed (maybe more than the current suggested nerfs tbh) and he'll go back to being at a 49-51% winrate, like he was when he had Presence of Mind + Coup De Grace / Last Stand.
He is definitely a champion that you can outplay of all the champs I do not see him as a problem.
According to op.gg Karthus is sitting at a 1.42% ban rate. I'm not quite sure how that's being banned every game.
Nerf Dark harvest, get rid of Prescence of Mind because KArthus is not the only champion who's going to be abusing that. He's just one of the first champions people thought of.
Presicion tree shouldn't have both PoM and all of the damage amps at the same time. It's not healthy.
