One further thought. You have to realize that spins are not one-mode, one- plane motions. Multiple modes may be involved. A complex, unknown equation is the mover in many fully-developed spins. This is why makes spin testing so difficult and scary in experimental aircraft, because you do not know what mode shape is in play. If the rudder cannot counteract the spin by itself, then you are in deep trouble because guessing the various planar rotation rates is impossible. You would know left or right spin and that's about it. Guessing a thrust-based recovery would be impossible for all practical purposes, and it would almost certainly aggravate the rotation.