So I’m very new to this game and just recently started, about level 40 and I’m following a spellbreaker build that focuses on cold shadow strike as its main skills and I see that it also takes up some dual wield tree skills as well as using 1H weapons. I was wondering if I were to equip a 2H weapon, would it benefit from those so call’ed dual wield passives (Dual blades) ? And also, would it be better to use dual wield or 2H ? Because whenever I see the DPS on the stat sheet, the dps would always drop 50-70% if I dual wield instead of 2H. Any tips? Thank you!
Dual is for dual. You won’t get any benefits from it if you don’t dual wield. Two handed weapons have their downsides, slow, sometimes even lower damage, one upgrade slot, while one handed are fast, sometimes have better damage, procs WPS, have two upgrade slots (if dual wield or with shield/off-hand).
Players mostly say two handed weapons are underpowered because dual wield is just way better; if you have WPS, two handed weapons are very weak.
Two-Handed Weapons aren´t necessarily best for Nightblade, otherwise they are a fine choice for many masteries/builds. Just to clear that up. I know USER_NAME_01 didn´t wan´t to diss Two-Handed Weapons, it just ended up sounding that way. 
I mean, I actually love two handed weapons and shields in general, and no, I didn’t want to say anything that sounded like two handed weapons are shit, I just wanted to say that dual wield is slightly better. 
Now we have Physical Reduction on Dual Blades zweihanders DO need some attention, maybe in the form of “Twohanded only” components?
I know you are suppoused to lose some defence when not going the shield route, but the gap between s&b>dual>2-H feels a bit too big.
I actually feel the same way. I mostly focus on S&B because I don’t like dual wielding and having a two handed weapon doesn’t provide enough to get it instead of S&B, in my opinion.