Xerath's ultimate doesn't live up to the fantasy of what it should be..?

It's supposed to be his final form, his ultimate state... I know the ult got improved visuals a long time ago but it just doesn't feel like it lives up to his theme of ascension at all. You'd expect Xerath in lore to literally make a thunderstorm and pump everything around full of arcane energy but it's not really possible to design something that chaotic to work in the game.. So what about a new champion that can actually transcend to a final form that makes an actual difference? Balance wise, that champion would have to have a significantly underwhelming pre-6 and bad damage but he\she would shine when they get to the point in the game where they can just ult and 2v1 against a gank easily or be at the center of a teamfight.. Kayn kind of has that thing when he reaches his peak performance when he becomes the Shadow Assassin but it doesn't feel too noticeable, more like an ordinary part of the game for him.

When I'm talking about transcending to a level of immense power\godhood, I'm talking about something like the one time when a villain called Kars became the ultimate being in the Anime show, Jojo's Bizarre Adventures (pretty sure that's the one)

So would that kind of thing be possible or is it just not an option because the balance department doesn't want to deal with a champion that has too much power concentrated in one ability?