I agree with that. Never doubted it. What I am saying is if you made a Spirit tube the same dimensions as an SL tube, they would both feel the same in the riding. They would weight the same, have almost exactly the same stiffness, and absorb road shock the same. Fortunately you can make lighter tubes with Spirit than with SL by safely using the less material. That makes the tube feel different. So it isn't the steel that feels different, it is the tube design.

OP asked if it was possible to discern different steels. My answer is no, you can't. But you can discern different tube designs, some of which are only allowed by certain very high strength steels. So if OP rode two different identical bikes with identical tubesets but made of different steels, as long as both bikes were strong enough to not collapse under him, he could not tell one from the other. No one could. That is the answer to his question.