It's only better than Lich Bane on champions who can shortcut the charge rate. It provides significant wave clear to mages at the cost of about 3000 gold worth of stats. That's only ever worth it if you get that entire value out of the passive. That pretty much only happens if you can charge it obscenely fast. It's not better than Lich Bane in every single way. Its cooldown is functionally 6x as long for most users and comes paired with an item that gives no stats on most champions.
The item's best (mage) users are pretty much only LeBlanc and Zoe. That said, it's clearly BiS on them. For champions like Kai'Sa it's clearly an intended option and just a strong item overall.
Yes, the item has an AP ratio. Yes, players are meant to figure stuff out and find interesting interactions. With Shiv you're paying for wave clear. That's pretty explicit here. The fact that it's taken over a month to show up (in solo queue; it was disabled in pro for 13.10) means the "if you just gave it two seconds of thought..." refrain isn't the zinger you think it is since apparently none of y'all figured it out for a while.
So yeah, the item has some champions who can really abuse it. That list is about two champions long to my current knowledge. And that should be fixed of course.