You seem like someone who studies this stuff a lot...what's your preferred SMG in HC? I'm an aggressive run and gunner but also play a lot of support (taking out air streaks and calling lots of uavs). Before I got my diamond SMGs my go-to was the vector with quickdraw + long barrel. Now I bounce between different SMG setups depending on what the competition is doing, but the majority of my classes are pretty similar:
Lightweight (switch to ghost for UAV-heavy teams)
Fast hands (was always partial to cold-blooded but haven't noticed a big diff without it)
Dexterity
Semtex + Flash
Launcher (so I can get away with no ghost)
I run quickdraw on pretty much all my SMGs and throw on long barrel when it feels like it's taking too many shots to kill. And this works pretty well for me for the most part, just wondering what you'd improve on.
I am the kind of guy who really gets into the nitty gritty stats and data when it comes to FPS games, so I know much of the raw data for the guns in this game.
I don't like SMGs for hardcore because I am all about extending that 1HK range as far as possible. If you play very aggressively, however, SMGs are fine since they offer advantages with movement speed, ADS speed, etc.
I wouldn't recommend you use the vector. I'd recommend either the PDW or MSMC over it.
This is why:
This is the dmg over distance for the Vector.
As soon as you hit the 22 range, it will take 2 hits to kill on hardcore.
Compare that to the MSMC:
or the PDW:
The one hit kill range for both these SMGs is substantially longer. In HC, 1HK is very, very important.
As for attachments, when it comes to SMGs I always run a combination of either silencer, laser, or stock. I prefer stock to quickdraw.
Stock changes the ADS movement speed with SMGs from 80% of normal movement speed to 102%...yes, you will move FASTER while aiming down the sights using stock on an SMG than you would not aiming down the sights. Pretty crazy. Your use of lightweight somewhat eliminates the need to have stock. I recommend you give stock a try though, either by dropping lightweight or combining it. Lightweight + stock allows you to ADS move at an absurdly fast speed that makes you very hard to hit. I do this on core sometimes, you can run circles on a guy while ADS and he will have a lot of trouble hitting you.
Everything else looks fine besides maybe dexterity. Check out the youtube videos that break down dexterity. Cliffs: The benefit is great on ARs and LMGs, not so great on SMGs. For third tier I almost always pick Engineer. Tactical Mask is great too. As is extreme conditioning.
EDIT: Just checked again, I was wrong. Stock makes ADS movement speed on SMGs 102%