Part of the issue is they changed it to deal damage based on maximum health rather than current health. The problem is %hp is always either underwhelming or overwhelming. It's tough to balance in a game like this. Right now it's blatantly overpowered. The way it was before was blatantly underpowered. There's really no middle ground for a %hp item, so I agree - it needs to be either remade or removed.
Currently, its strength comes from your own ability to refresh it and stay alive while it eats away at the enemies. Champions like Amumu, Cho (spikes proc it) and Singed are ridiculously good at this. It's far less useful to a bursty, squishy mage. "Pokers" are another story entirely.
The whole idea behind the item was to give mages something to counter all the bruisers on TT, but it just made the tank/tanky mages that much more powerful. The squishier ones having problems don't really benefit from it.