How is it that my builds never match damage as advertised?

Homefully someone here can help. I have a running issue where I get insane builds such as the Big Ducks Kinetic Bolt Deadeye with very if not near-exact gear, match the calculations as best I can in Path of Building and yet my damage is a fraction of their POB. In this case, his POB (https://pobb.in/QC522cJTE7Yn) has 1.5 BILLION DPS. My POb (https://pobb.in/jyQMfUzKb_ZX) has just over 7 MILLION?!?! How is that even remotely possible?!?!?! SAME gear, SAME configuration and yet I have laughably bad damage. This has happened to me countless times and I was wondering if anyone here had any ideas. This is even a build of mostly uniques so little room for variance and yet here we are with 100s of DIVs invested and nothing to show for it. As I said, I have followed dozens of builds over the years and not one has provided anywhere even NEAR the damage as advertised.

Your wand is only about half the damage of the other PoB you posted but the biggest difference is that you are only calculating the outgoing dps, their PoB is calculating the dps of all nimis returns, not merely the initial projectiles you attack with.

I appreciate the information however, POB shows that wand (when I put it in their POB) at around 30 million less, not 1/2 but let's say it is, 750 MILLION is not 7 Million. Also, I copied calculations as best I could so where is the ability to calculate returning that I did not see? I see I missed one calc and that raised damage to 12 million but we are still so far off.

Ok, nevermind. I found were they claimed there was 121 projectiles so that is how they go the insane damage.