I get the desire to have it be a grand adventure, but, and maybe it's just my preference of deep but narrow as opposed to wide but shallow games, this one city has so much to explore even just as a concept, a la disco Elysium or Prey or Dishonored or the new deus ex games. each of those has one smallish location that is super in depth with secret paths, stories, history, etc.
then the city could have been bigger, if you want to just transplant the area in, or richer, if you want to make the space there already is deeper.
like just off the top of my head you could have different Burroughs of the city as areas you explore or unlock or whatever with the poor ones being infested and you could see first hand and through gameplay the corruption and failure. Have there be quarters for different trades, a magicians quarter, an artificers district, etc. have an area which was once wealthy and had lots of wizards but something failed that lead to it being corrupted, and so all the rich fled and it's now a shanty town for the poor who get killed and slaughtered while trying to survive. layers of buildings on top of buildings, marble facades covered up by shacks hung to them by scaffolding.
And the game already has the best trope of city design - the inhabited bridge with houses on it. fuck yeah