When you get a free 20% damage reduction for everyone around you, and you only pay 30 mana a second to do it, you kinda create the best anti-teamfight champion in the game. Gating how long you can hold it up for would be the most logical move if you want to hit his tankiness without hitting the actual numbers or, lord forbid, forcing him to target an immobile area again.
I'm kinda surprised Xerath's e hasn't been nerfed yet. It's a pretty easy to land (slightly faster than morgana q with less of a tell and about the same range) 2 second stun at level 1, which screams of a future of being shot with the nerf gun. And he's been getting the professional attention that usually causes rito to pay attention