If you throw in stock then you are way more lethal. The faster you are on target the better. If you pull are on target faster than anyone while being hard to hit, stock, and you don't have major visual kick, toughness, then you will win most of your gun battles even with the lag. I know many of you don't like dexterity but it is invaluable and used often for a reason. Even if you are camping somewhere when it isn't useful when someone does run up on you while you re-position dexterity can be the deciding factor in keeping your killstreak or losing it.
This is all my opinion of course based on trial and error. Plus when my friends recommend what to use to do better and I tell them this their scores increase greatly... Depending on the skill I guess.
I knew FMGs would be OP before the game came out: http://www.gamefaqs.com/boards/995751-call-of-duty-modern-warfare-3/59204323
It's because stock and quickdraw were perks in the other games, and (imo) should have been perks here, but for some reason Treyarch decided to make them attachments, and instead make perks like hardwired and fast hands exist.