When you craft things their power level is based on the highest power level you've seen on an item. For a crate, the items are in the range of that number +- 10, not sure about crafting. YOu can also upgrade an item to the next rarity with scrap, but it won't increase in power level.
Veteran takes a bit of getting used to, and your level 10 and 15 skills will help out a bit. If you're playing as Sienna and haven't already, I'd highly recommend checking out Pyromancer and unchained. Both are improvements on her base class, with Pyro being straight up top tier with the right gear (crit gear, cooldown on crit, lose overheat on crit, and a bolt staff for spam). Pyro's hero abilty is a homing bolt that will one hit specials or several storm vermin or like a dozen slave rats. It's nuts. I haven't played much unchained, but its apparently pretty good too (although it has a bug atm that if you get downed by a hook rat or assassin rat when you get revived you will just overheat and die because of the accumulated damage. Absolutely awful on higher difficulties where teh downs matter).