I don't find CK is really all that much outside of his ultimate. Leoric will always be terrifying because he can commit in a way no other hero in the game can. People fight and die over aegis because it is just that game changing, and this guy gets a free one every 60 seconds. Actually, his is a super aegis, he doesn't spend as long on the ground and he applies a pretty heavy slow to anyone trying to camp his grave. Leoric's crits are also much more reliable than CK, and his stun might as well have no cooldown. Adding a projectile speed to chaos bolt was the change necessary to bring CK down to average, in my opinion. I still find Leoric one of the best heroes in the game if built properly. With items he really has no counter, your options are to simply outfarm him by a lot or end the game before he gets items. The change to shadow blade giving attack speed has actually made it surprisingly good on a hero like Leoric as well, nothing says "f*** you" like popping out of stealth in the middle of their team and two shotting someone, only to get back up after they blow three ultimates on you.
But I digress, any hero with items is good. I compare carries to their maximum potential unless their early-mid game is something noteworthy, such as Viper, who might die down as the game goes on compared to others but has an absurdly powerful level 6-16. CK might beat Leoric at ganking. I think he certainly loses in team fight initiation.