I can safely say something is wrong with your game. I'm currently playing a Sargo class for one, and it has a distinct model.
No config editing whatsoever should be required.
One thing to keep in mind would be the starting date. If you play the early campaign or use the mission editor to set up a mission in 1941 or even 1938, you're not going to get any later sub classes.
Try a 1943 or 1944 campaign and see what choices you get. Otherwise, sounds like your game install is borked.