Wow, can you read at all?
First of all, as has been said ad nauseum, Commander is not an actual rank. So the story hasn't revolved around it. I can't remember a single time anyone ever called me Commander.
Secondly, as I said ... in the grand scheme of things there aren't that many Darths ... there's one. If someone were to write a book covering the major stories of this game like Revan did with KOTOR and KOTOR 2, then those stories would be condensed into one person per starting class. So the number of people who have a Darth title has nothing to do with whether or not we should get Commander. That makes no sense.