Once again Riot misses the mark with Karthus nerft
No point in running him in lane now, thats for sure.
The nerf was idiotic, as is typical of Riot these days.
The problem was the Dark Harvest rune, or his general ability to clear jungle fast.
You basically nerfed him because you didn't want to do something to just slow his clear or do something with dark harvest---such as let it scale better but it only focus the lowest health champion when targeting mutliple enemies simultaneously