first of all the benefit of the level geometry is the bsp management, so also pretty huge indoor levels(or cities etc...) are fast.
Another benefit is that with the lightmap. That you can't do with models, because you can't give them a 2nd uv set in a6/a7 => you need large textures, where you baked the lighting.
The deficits of bsp-management is, that your level can't be that complex, becasue for every little details the bsp-tree bcomes more complex( just make some hight detailed level and then look at the little red lines if you press 2x F11)

so the best way to make it level in a6/a7 is probably to build the main level with blocks and then add a lot of models, to make it high-detailed (i think the unreal engine(2?) used also such static models for walls, to make it look hight-detailed and deal with a good fps)