Construction sets for dungeons = cookie cutter dungeon design again.
Well, it all depends what is meant by "kits".
Oblivion' CS didn't have it, but if you open Fallout's GECK, you'll find some cells with prefab vaults and building interiors, which could be copied and pasted from cell to cell. If that is what is is meant by a "kit", then chances are you'll be playing the game and have a sense of "deja vu" every time you enter a building. I guess things like office buildings would feel generic anyway..
Now, if by "kits" it is meant the distinctive groups of assets for interiors, that is a different story. Unless the cells contained the prefabs were removed, Oblivion dungeons were entirely "hand-crafted" (don't know if lovingly). Even the Fallout prefabs were only floors, ceilings, and walls: all the details (lights, furniture, pipes, etc etc) were placed by hand. And most of the prefabs weren't one mesh, but a number of meshes put together
In Oblivion, the distinctive groups of assets are pretty large in number, and these aren't broken down like "room1", "room 2", etc. You have a number of different modular corners, a number of different wall chunks, ceiling chucks, floor chunks, which all snap together in every direction, so they can be used to create distinctive dungeons.
And yes, they all are created by hand.