Is xerath considered good late game?

Xerath is at his weakest during the early game IMO. That is when he can get ganked, when mana is still a heavy disadvantage and before he can siege for turrets.

Late game he has some CDR, great AoE and scalings, mana regen and he becomes a damage dealing god that can win games with a stun that manages to land on a squishy.

Xerath is fine late game. He has trouble early game because he needs items to scale, but once he has them, he does alright.

good early, mid and late game, yep.

Well considering his ult practically one-shots ADCs if he hasn't fed to high hell, then yeah he is fine. If fed, he is an absolute monster.

But don't play him, knowing Riot, he will be nerfed within a few months.

Extremely good. yes.

a 0/0/0 200 cs xerath is a nightmare late game, so that tells you something. 0/0/0 pantheons or rivens aren't so scary, they need to keep others down to be good.