Hi!
It is not the modelling or creating the terrain that is a problem in 3DGS, but the management of the texture, for create a terrains could be used any program from smallest up to biggest, but the more important thing is the texture and the shadows!, the texture should be seen more detailed, I don't say that I want see the ants that they walk in the grass, but to can distinguish a stone in the grass from a colored stain, or the grass self ! more detail in the textures please...

greet
salva