I agree, spokes do only support a load in tension. But that's why it's valid to use vector analysis to resolve the tensile loads in the spoke. Vector diagrams are a valid way of analyzing angular forces by breaking them down to components. In particular when the resistive force (the spoke) is not lined up with the applied force due to retaining factors. In this case the rim and the hub.

In your rope example if you have a weight hanging on a rope and you push the weight sideways in fact the tensile load in the rope DOES increase. It becomes a vector addition of the downward force of the weight plus the sideways force and it adds up the same as shown in the triangle of forces for the spoke.

In fact your rope example is the whole basis of the increase of tension in the spoke due to the shift away from a true tangential angle that I show in my diagram. I suggest you find go find a mechanical engineer and ask them about your rope example and see what they say about the increase in the tension in the rope since you don't seem to like my explanation.