> Just take your elbow and angle it to 90 degrees, then rapidly close it so your upper and lower arm are (almost) in parallel.

That's trivial with the modern flat motors and position feedback. In fact, motors can do it faster and with more precision than we.

The only reason it was ever hard was because motors didn't have a lot of torque/volume.

The reason our muscles come in pairs is because they can only really apply force in one direction. Motors don't have this limitation, and don't need to be paired.

Anyway, motors still don't have enough torque density for making fine manipulators, and the lack of sensorial data will still stop you from interacting well with the outside world.