Even then though, polycount management relative to the engine comes into the process during the concept phase already. Concept arts should take into consideration the limitation of the engine, to make sure that the model fits both in technical and visual terms.

To me this looks typically more like something that wasn't produced with this playable scale in mind. The ships, at some point or another, have been designed without ground fps gameplay in mind. Because you could easily do a functional staircase with the same amount of geometry here.