I think it sounds like you've been paying attention and appear to have good critical thinking skills. The SG is limited in any form of combat for exactly the reasons you stated. Short range, bulky ammo, high recoil. This does not mean that the SG is totally useless, just that, it's limited.
We all know that the SG is a dandy HD tool. Inside a house at short distances it can be devastating. If one has to step outside for any reason though, he would be better served by a carbine. Range is increased, ammo is lighter, and the weapons are lighter.
That the Military uses the SG to good effect means little to us civilians. The military sends out a group of men (from how it sounds from other posters, one would have a SG and the rest have rifles. Think about this. If you have a lot of friends that are going to be with you, perhaps one should have a SG. If you are a very small party, or alone, then the rifle is the best choice.)
Or so it seems to me. YMMV.