I think I did not made it clear.
Outerra engine process bulk data into a 3d world. The limitation of that technology is the fact that you have anyway to place 3D objects manually thru additionnal sceneries.
So by the end of the day you have two options :
Bulk data -> engine -> 3d world about whatever the engine can do with bulk data
Bulk data -> human developper -> 3D world. More time consuming, more accurate, detailled and living world.
Simple fact is the amount of scenery done for FSX, while FSX can render the entire world, its innacuracy, despite wide range of tree/houses/random 3d model, can't make the place believable. That is due to the procedural rendering engine vs prebuilt scenery engine (or whatever they call it in english).