Xerath should probably get a new passive
I'm not going to be that guy that calls it "boring", but the only reason he even needs it is because his [Q] has a massive mana cost. Quickly comparing it to Ziggs' [Q]: it needs 70% more mana when it already has less of an average damage output. And Ziggs has more base mana than Xerath does.
Ziggs has continuously overshadowed Xerath, so he really needs a change. Open to suggestions and analysis on his kit, because it's debatable which direction a new passive could/should take him.