They're crap at a distance
But yes, they are strong up close. Part of it is the maps, part of it is the modes (Hardpoint is all
kinds of SMG friendly), and part of it is that the ARs and LMGs don't blossom until you level them up, and some of the later ARs are significantly better than the early ones.
Pick an AR you like, level it up, take Toughness, slap a Target Finder on it and keep SMG users at arms length - you'll find they can't do squat to you.
Of course, depending on the map and mode, that varies from 'a bit challenging' to 'god damnit, shot in the ass again'.
Which is another issue of the current leveling curve - once you have Scavenger and Shock Charges/Claymores/Betties, you can actually set up a defensive area again.
The lack of footstep sounds is also part of the problem.