When a city generates in an area with extremely high terrain (extreme hills, or a custom generator), the entire city level is locked at y=95, which can be 30-50 blocks of blocks below the surrounding terrain, leaving the city in a blocky carved-out valley hacked into the mountain

In terrain like this, the entire city would benefit from being moved upward several more city levels to fit into the terrain better. For example, a building placed on a mountain plateau with biome level 130 should have a street level of +9 or +10 (y=131), instead of the current maximum of +4 (y=95).

It would also result in more interesting streets on steep terrain with more steep staircases and terraces. The "mountain" city in the images above is completely flat and level because all of the terrain is locked at maximum.