2h engineer does not have good survivability compared to 1h+shield or dual-wield, 2h sets offers no direct survivability, sure they might offer the usual of +hp, +DR etc, but what you need is a way to regain hp or to avoid hp loss, none of the 2h sets offer that, and you WILL die more often if you use a 2h build.
You also get 2 more weapon mythical sockets when you dual-wield, and 2 more armor sockets when you use 1h+shield.
For Derinkuyu and Trolls any build works, and any items will get the job done, but for Darkness Falls a 2h set will get you squashed as they are not very well put together when it comes to survivability, they do have the dmg, but not the survivability (compared to 1h+shield/Dual-wielding).
So what makes me say that? lets compare T1 sets
2H set viable for Engineer: Savage Draconic
Adds ~900 Health per second as set specific survivability (super duper crappy, does nothing), and the ability to proc the Parry effect. Can never facetank.
1h+shield set viable for Engineer: Smouldering Brimstone
Adds the ability to block, which combined with dodge is 97.5% chance to avoid damage, even when a boss uses hes shield ignoring skills you will have about 6-7 times better survivability and with a shield you can facetank a boss without fear of death (when you min/max your gear)
Dual-wield viable sets for the Engineer: Residual Aftermath
Adds the ability to leech 8% damage done as life with autohits and also adds the chance to proc the Parry effect. Can facetank all day and wont die at all when min/maxed your gear.
All 3 sets reaches 100% crit chance, 500% crit damage and does about the same dmg (since 2h only have 2 sockets), but the survivability is great when using a shield, and even better when you dual-wield, 2h just cant do anything to help you survive while 1h+shield and dual-wielding helps you immensely, as of right now, you will NEVER be able to fearlessly facetank with a 2h on an Engineer(you cant really facetank with a 2h build since you will die often due to no way to regain health fast and not a high chance to avoid damage), the only thing you can do to add survivability as a 2h user is to get more health, thats it.