Instead of using the landscape tool, you create individual meshes in your modelling software. Then put these into your world as static meshes, to represent the landscape. Or cliffs, or mountains, or river creases etc. By doing that you enable better LOD control, better resolution control, better level streaming, better material control, better? general performance AFAIK.
Clearly, you don’t have to only use meshes, you can combine meshes with the landscape tool. Also you don’t have to make all the meshes have the same resolution. Larger flat areas can still be less dense than the creases or local bumps. It’s up to you at this point.