Where did you pull these numbers from?
If you just look at a wall larger than 16x16 blocks, that already has more than 500 triangles drawn. If we look at, for example,
this screenshot, it has easily over 25000 triangles drawn on every single frame. I don't know about Crysis, but I doubt it has as much triangles drawn - where it needs performance is all the post-processing, which is quite constant time.