Xerath is stronger laner if you hit every fucking Q, and much much better poke champion. I laugh to people who compare Vel'Koz with Xerath poke wise lol.
Vel'Koz is better teamfighter tho, he is also easier to play and forgives more.
Xerath can carry so fucking hard and tilt enemy to death. He is more annoying to deal with. But It is balanced with being one of the hardest champions in the game.
You can kill full HP ADC from +5000 range with only ultimate, not even 5th is needed. I killed a Lucian who had full stacked Bloodthirster shield with only 4 arcane barrages. His ultimate deals insane, much more than Syndra ultimate, but harder.
In this meta, I highly recommand Liandry + Deathfire Torch. Thunderlord's Decree is useless shit.