User blog comment:ClariS/Why Xerath's Passive is Bad/@comment-99.55.245.182-20130317160736

Xerath's passive is actually great- there's not a lot of armor options for AP characters. Outside of Armguard, there's no item that would fit him that would provide armor. His passive helps him fight off ganks. Imagine this scenario- he's in his Root, casting spells from a great distance and dealing good damage. Then, in the middle of his combos, he gets jumped on from the bushes by a Rengar! Without his passive, Xerath would go down faster than a ton of bricks. He'd be stuck in his root at the first attack, and with Rengar's high AD ratios, he'd get run down pretty quick.

Or, say he gets hit by a Xin's E. Xerath would melt. Or say he gets stunned by an Ashe's ult, mid root, and then she attacks you. Or Riven combos into you. Or Jayce gets to you. Or, really, an AD champ gets to you. Let's say Yi, for example. He turns on Highlander, to escape the stun (in a way) by still having high MS. Then he comes in and AAs you to death.

Without Xerath's passive, any AD champ would melt him in an instant when he's rooted. To have so many champs as counters would be stupid.