Deathfire Grasp, Morellonomicon, and "Support" Mages
A looong time ago, they removed Deathfire Grasp, an item that granted 120 AP and 10% CDR, with an active that increased magic damage to the target by 20% for 4 seconds. Mages were forced to be balanced around the item.
Fast forward to the current version of Morellonomicon. It grants 400 mana, has double the cooldown reduction, restores 20% mana on kill, and still kept the grievous wounds passive. And costs 200g less.
Maybe they wouldn't have to nerf so many mages into the support role if the first item they buy at mid didn't give high amounts of everything a burst mage could ask for.