How do you know the brain separated from the rest of the nervous system and body would still be sapient, capable of thinking and awareness? There's an assumption you're making that the brain is all that's needed, but the nervous system extends throughout the body. One can argue sensory organ are part of the nervous system.

Embodied cognition rejects this assumption. We didn't evolve as brains that were then put in bodies, we evolved as bodies with nervous systems.