It's sometimes confusing to see how one weapon might have better stats than another, but seems to do less damage.
Usually, the confusion is caused by the Damage Per Second (DPS) numbers. The difference between the DPS numbers and the Actual Damage numbers is partially due to the speed of the weapon. Some weapons are faster than others.
On Faster weapons, the Actual Damage PER HIT is lower than what the DPS shows it to be, because the DPS is an average as determined over a long period of time. If your weapon hits faster than one time per second, then in one hit, it doesn't do an average full second's worth of damage.
Weapons with a high Critical Hit percentage will also seem to do less actual damage per hit. That's because the DPS includes critical hits. Critical hits are typically about 150% of the normal damage. So if you have a 10% critical hit, and your DPS is 10.5, then assuming your weapon hits once per second, in ten seconds, you'll hit 10 times.. only 1 of those hits will likely be a critical hit. So you'll do 9 hits at 10 points of actual damage, and 1 hit for 15 points of Damage. (9x10 + 15 = 105 = 10.5 x 10 seconds)
By comparison, if you used a weapon without a critical hit and did 10.5 DPS per second, with no critical at all, you'd hit for 10.5 points of damage with each hit.
In this example, the gun without the criticals would appear to be doing more damage, and it WOULD do more damage on every hit except when compared to the criticals, but over the course of time, it would actually do the exact same average damage as the other weapon did.
In the end.. the DPS as it appears in your bag is the ultimate ruling factor regarding how much damage a weapon will do in the long run. You could consider most elites and all bosses to be "long runs", however, having a spike in damage with a critical, CAN kill an enemy quicker if they happen to be low on health at that time.