Like Clint Smith used to say, when he worked for HK: 9MM buzzguns will be replaced by rifles.... and they have. 5.56 is much more deadly, and CQB-Rs are compatible with regular ammo, perfect for cross loading. As I wrote in my introductory post, the disadvantages of short 5.56's are being overcome.
People spend too much time worrying about terminal ballistics and not enough training. Most people that I know, or know of, are satisfied with the terminal effects, assuming they made their hits.
Just like sub-guns, subcarbines are used in a peculiar fashion. You stand on the targets toes, put the m uzzle in his ribs and let him have it, so to speak. <----- Not entirely true, but you get the point. As bigbore said, they are a putter. When you go out to play your short game, take the right tools.