"we want to reward players for fully charging abilities."

So you nerfed Janna Q every patch because "we want to push people away from double tapping Q for an instant tornado, so we're makin it weaker initially but stronger when fully charged" (they actually nerded both, but we'll ignore that for now). So why does Xerath, the "poke mage" (HAHA poke. Lmao) not have the same treatment? Lux was nerfed for being "too safe" even though she has half the range of Xerath, and less move speed, and she doesn't have a stun, and she's insanely mana hungry, which Xerath has never had an issue with... I guess what I'm trying to say is that Xerath is too safe with no clear weaknesses. There's no drawback to instantly popping his Q, like there should be, and because it's not a projectile, it's just that much harder to play against. When they first released the rework, Riot said that his passive would force him to play closer, giving the enemy a chance to hit him back, which you can't do at any other point because of his range and safety.

TLDR; Xerath is too safe, his Q needs to be weaker when he doesn't charge it up.

Edit: I forgot to add, Varus Q is pitiful if you don't charge it up- like it SHOULD be. The range and damage increase as you charge it up. This is exactly how Xerath Q should be.