You're acting as it was physically possible for them to have made a city like that. It would have taken at least two years longer to finish Oblivion.
And you said it yourself, the pge barley even described it anyway.
This Imperial city crap is getting old. It just wasn't viable. And, the pge is not immaculate.
Perhaps it wasn't viable, but if it wasn't, it was indeed due to time constraints. Some things just had to take precedence, I suppose. Like coding Parallax mapping into the engine, deciding that
it wasn't viable, and removing it again. I suppose you can't ask them to do everything.
Cell-design is probably one of the least time consuming parts of using the CS. I speak from experience. I take meticulous detail with my cells, and none of them have ever taken me more than two hours to build. It's even faster if you have detailed concept art and plans for the cities. Bethesda did. They just didn't use them. It's plain to see that Oblivion was poorly designed in most respects.
Don't know how immaculate texts enter into it, really... but the PGE made Cyrodiil out to be a holy utopia, and the Imperial City a city of splendours.. Oddly enough, that's not all too far from how it was portrayed in-game. Except for the city of splendours part.