The problem isn't "realism" per se but a consistency of aesthetic. Here you have a modern (but disturbingly empty) Gotham that seems high tech, albeit bland. There's little character to the city, its quite obviously just a backdrop. And THEN there's a castle on the outskirts, no explanation, a total clash with the city as a whole. And again, the castle is unexplained, why? Because the settings are just backdrops, just stages for the characters. They aren't made to seem like actual places, nor are they given a consistent aesthetic (compare that to BTAS' gothic noir feel, which even the fantastical locations were able to fit in). Its all very generic.
So there's a castle on the edge of Gotham. A generic castle. Meh.