I think you are imagining the twisting force between crank and sprocket during torquing to be similar to that which occurs when the engine is running where torque is applied to the crank by the expanding burning gases and the sprockets motion is resisted by the inertia of the pump, cam and accessories. Nothing even remotely close to those opposing forces occurs during torquing where the torque is applied to the bolt instead of the crank and the crank and sprocket are held solidly together by the friction on their mating surface. While tightening the bolt, the only opposing rotational forces between the crank and sprocket are the rotational force put on the sprocket by the friction between the face of the bolt and the outer face of the sprocket and the rotational force put on the crank by the fine thread ramps of the bolt/crank interacting. Both of those forces are minuscule compared to the MUCH greater force of friction between the face of the crank and the inner face of the sprocket. No matter which you hold, the key locates the one in relation to the other and no matter which one you hold you aren't going to damage the key during torquing.