Blood mage isn't overpowered its just overpowered items and spells
It's not blood mage is just the skill itself. In my opinion in a 2-4 week grind the build should be at 90% peak what its capable of. A capable build usually does somewhere around 20-30mil dps this seems high to some but this is just how it is. This league both CoC and Poisonburst but probably many other builds capable of this ballpark dps. Looking at perspective of previous league. LA Deadeye did somewhere around this ballpark and any capable build. It's actually take a lot investment on the CoC part to reach around 10m comet. And if I would go for a nerf i would nerf the ceiling and not globally. It shouldnt cost like 20 mirrors to reach "nice damage" so we don't want to move up the goal post for late endgame. Just a ceiling nerf. Also this league added a few ridiclious mechanics that also enabled super overpowered build not to the fault of blood mage. Paired with a new vaal cultivated orb corruption on: Atrziri Splendours, Rathpit Globe AND Vertex for +4 skills this is just a recipe for game breaking damage buff. We've been here previous league too where Commander constrictor gave you like 150% increased damage insane AS etc.
