Thank you for sharing these videos, they are perfectly illustrating the point!
I shall add after watching the interview with Lionel, which I personally enjoyed a lot watching (and I thank Lionel again for his sincerity and openness in sharing these technical details), the problem with the “shape retention” might have a much simpler explanation now.
In effect, if I understood correctly, they are optimizing the rendering of mesh in “skipping” vertices (sorry if this is too technical)! They seem to be using the index buffer for this which in turn would tell the GPU to only render this or that triangle, instead of both (just to keep it simple). In this case, it is no wonder you get non-shape preserving mesh LOD rendering because you’re essentially cutting through the shape, instead of displaying a lower polygon count of the same shape.
Sebastian hinted (I believe around Dec. 2020) they were (re)implementing their task scheduler for handling tessellation in a more effective way. Maybe they are not just done yet with this, or actually what he meant back then was just to handle this “index buffer manipulations” in a task instead of in main thread. Only Asobo knows.
My engineering side is wondering whether they are not using Simplygon because it didn’t deliver, because it is not suitable for this, or because for example they now have better solutions. One thing is certain here, the current implementation is not shape preserving and this is really distracting.