"The Black Cleaver debuff counts per target. Multiple The Black Cleaver on the same champion or across multiple champions will only apply stacks of the debuff faster, but the max cap will still be 4 on each target."
It's like people only read the passive on this item. --- http://i.imgur.com/cuYAp.gif
This is great until people realize that building health is easier and cheaper when going tanky. This is pretty much the only way I think for AD casters to be a lot stronger. I think the problem is that a lot of strong bruisers can go for this as well. This build is amazing for bruisers with attack speed buffs like Fiora or Lee Sin.
I think you probably think it's too strong but I imagine no one you thought would know how to counter stacked items, which we haven't seen in LoL for some time. --- I come here to argue!