Assuming, that it is coherent to talk about the "territory" of morality, I think I agree with your paraphrase. But I expect that certain maps are likely to be useful much more often.

I think that classifying types of reasons actually used improves our understanding because it cuts the world at its joints. It's subject to the same type of criticism that biological taxonomy might be subject to. And if you go abstract enough, things that look like different kind merge to become sub-examples of some larger kind. But at some point, you lose the ability to say things that are both true and useful. Like trying to say something practically useful about the differences between two species without invoking a lower category than Life.