Tessellation can cause FPS to drop, I actually stopped using it on all my projects, only normals for now, it´s even works if you use tessellation on landscapes.
Nanite has other issues, but I’m sure Epic is working on them, if not, the engine would already be released.
Still I believe it should stay in UE5, why remove it… or anything that previously worked fine in UE4, it just adds more possibilities to the engine