On the SMG vs shotgun, I will tell this one on myself. When I first got a Thompson, I had the same discussion with a friend who had an Auto 5. So we set up five silhouette targets at a range of, I would guess, seven yards, in a line about a foot apart - bad guys ganging up on us.
I put a 50 round drum in the Thompson and made like Al Capone, just like in the movies. The "trench broom" and all that stuff.
Then he upped with the Auto 5, and rattled off 5 rounds of 00 Buck.
The result? I had gotten one (1) shot in the edge of the first target. Period. No need to change targets. He put 9 slugs into each target and did it faster than I had fired 50 .45 rounds.
Later, I learned to use the Thompson better, but that little session proved to me that there is nothing about a subgun that will make holes magically appear in a target.