it’s not just the weapon, it’s also the Skill, Natures, Talents, Hero Points in the Skill used, affixes, Sets, Myth Stones, Mythic affixes…
I know that many of the new posters on DQ are looking for a billion damage, 100 billion, even a trillion+ damage build. it has recently gotten me to wondering if I can get a Comet or Barrage to have a billion+ hit without Crushing Blow. I think most billion damage done is with Special Skills, usually MH Special Skills, but I think I’ve seen some OH Special Skills get a billion+.
the thing to realize is that if you know everything on your build that buffs damage, you can plan out on paper that billion damage. just make sure that it’s possible with the Items in the LegendEx, and that you can Jasper Items from one Class to another if you nee another Classes Items.
on a last note, one thing many players forget for damage is the +/- 25% random damage. so after you figure out all of your damage (which would be the average damage done), multiply by 0.75 for the low damage and 1.25 for high damage.
the DPS formula is in the Codex, and I did a post on it 
hope this helps.