Skeletal meshes and their supported counts are an interesting problem in real-time graphics, especially as the technology’s been evolving lately.
If by skeletal mesh you mean NPC as a whole, then that can be a complex puzzle. An NPC’s programming stack can have massive implications on perf, whether they’re designed to stand around and say dialogue vs. move/collide/fight the player intelligently. That can have both CPU and GPU ends. Then there’s the asset itself, which depending on polycount, rigging method, texture programming/animation and more, can also have a wildly varying cost. On top of that there’s ray-tracing, for whom skinned meshes of any sort are incredibly costly because you have to constantly rebuild the acceleration structure.
While I couldn’t speak for Cryengine, I know Unreal has parts of this pipeline covered under defaults, others not. That being said, I’m not sure how easy it would be to tell what aspect of perf is an engine’s fault or a developer’s implementation.