User blog comment:ClariS/Why Xerath's Passive is Bad/@comment-5764133-20130318113236/@comment-4881935-20130319040051

that's why you need to maximize your range boost. Abuse every last inch of it so you don't put yourself in a position where the enemy can jump at you with ease.

And secondly, he doesn't have to stay in his root place for long, and along with the 35% bonus movement speed, you should be able to keep yourself at bay with proper placement.

And about the last bit, that's really opinion based and if they did add something offensive, I would suspect them to change his offensive abilities along with it.