I play bot lane almost exclusively and tbh the only thing xerath has going for him is that not many people have matched up against him. From playing against him I can say that he quickly crumbles against any aggressive match up. His ability, locus of power, rewards him for remaining stationary.
the act of not just being stationary but communicating it to your opponent with animation is an invitation to land skill shots and lay down aoe spells.
This isn't to say that he can't be effective, just that, unless he is amazingly well played most other bot lane choices will prove to be better.