I think electric motors are just barely suitable for mobile / humanoid robots. Compared to human muscles, they're heavy and they overheat quickly. Current humanoid robots are spending most of their energy in carrying around just themselves, which is a huge amount of dead weight, while being unsafe for anyone to be around.

If someone invents a new type of 'artificial muscle' which has low inertia, high force/torque density, and can work without overheating, that would instantly kill all other robotics companies.