My point isn't whether N'Zoth is better than UI, but that complaining about UI based on its value for mana cost is absurd.
You literally asked the question:
Is it better than N'Zoth, for example?
But beyond that it isn't that absurd to evaluate UI based on the value of the things the card does, because those things always happen when you play it. Whereas something like N'zoth requires setup and the value it generates is different each game.
It's like CotW and that was overtuned when it did 50% extra for the mana cost. UI does 75% extra worth of stuff for its mana cost.