You say most people learn better with step by step instructions. That's a way of classifying people. Why is that any different then classifying them as an S?

Okay, you have a point. That is a classification.

The difference is: I'm not drawing an inference that "because they learn better with step-by-step instructions, then they will also have other specific but unrelated personality traits that go with it". I think that such inferences are dangerous when dealing with something as complex as the human brain.