In the past I created a complex terrain per mesh tools and T-Spline. The result can be seen in the old thread here:
My workflow was that I created a mesh of lines, converted the lines to a mesh object (per t-spline _tsFromLines), smoothing the mesh per catmullclark smoothing from weaverbird (Weaverbird – Topological Mesh Editor | Giulio Piacentino).
I used the weaverbird smoothing because in the past there was a T-spline problem to keep edges unsmoothed (solved per T-Spline 4).
I feel good to create the terrain per drawing “mesh” lines, perfect to control, best for adding details where needed. The T-Spline job isn’t a big part, maybe you can create the terrain with standard mesh tools and the weaverbird smoothing only. On the other side, if you create terrains often, T-Spline offer you more flexibility to create and modify the terrain.
I found some old screenshots from the project some years before.