What we see in the image is the classical painters approach, you only need to paint Grass where color changes and where it influences the silouhette.
It depends heavily on the Camera Where you need some Grassblades and where not. But maybe its just as simple as turning the numbers down, for example using 100 instead of 5000 in the density settings.
My current idea is to use weight painting for populating the ground plane just on the spots where we need it to be populated. So you basically place everything else and then simply paint grass in where needed. Combined with some Ground Texture this could be a solution at least in my head.
