I think we must wait for realease, lot of optimisations are not done and many things not available,
as workflow it’s work in progress.
Perhaps the release will proove Nanite meshes can be smaller than 4K and 8K baked normal map versions with LOD (no LOD means less in game Ram to store LOD).
If equal or smaller disk size needed with Nanite, better go for Nanite and big advantage is movie quality.
All your answers in Brian Karis Nanite explanation
Huge amount of meshes and impressive level of detail.