This is one of the most comprehensive workflow Tutorials for Landscapes in blender.  He talks about how to blend textures, use meshes instead of displacement, and using lattice for randomness.   If you watch this video 3 times, first take the info in.  Second, take notes, third, Try different parts using his Add on. (free version)

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This was made with ai not blender. Davinic to edit. and music maker for the music.