Xerath could be like a video game boss...

If you tweak his ult the right way. Here are my suggestions: 1)50% less damage taken and immunity to all forms of CC BESIDES knockups. 2)Cannot use ultimate charges any less than 550 units outside of his casting position.

Here's a diagram to illustrate.

https://embed.gyazo.com/86ece8f6b457616a88690e51734ab87f.png

Now, Xerath's ult gives everyone full vision of him, making it so its very risky to even attempt using ultimate, and against good teams, almost impossible, as they will find a way to get to you ASAP with one of their assassin-like champions. This is one of the main reasons why Xerath lacks any competitive viability: dive potential on him. Him especially, as he has to make himself fully immobile. This change would make it so that he'd have some nice durability to help keep his ult up, in exchange for not being able to directly attack anyone whos near him while his ult is up. I also think this helps Xerath thematically as an omnipotent being; I think of it like a videogame boss:

You have this giant machine of a champion, scouting the entire rift for pray from afar, but everyone can see him. Everyone knows the objective, so they fight to get to him through the barrage of arcane. Once they do, they realize that they must break through his outer shell in order to kill him, using his main weakness: a knockup. Xerath goes into a frenzy, shooting off his abilities mindlessly (this is what anyone would panic and do at this point tbh), but he is able to be downed quite quickly.

IDK, I just think it is a lot cooler, and I don't think it is overpowered as Xerath can't just stuff his ult charges onto people right next to him. It's an interesting tradeoff and I think it would help Xerath to have atleast some competitive viability, because right now hes never gonna see any play if he doesn't get some form of defense or mobility LOL.