Appears that the orb DPS difference occurs because you have Sorcery talent on the 1st legend. Change the 2nd legend to same talent & I believe orb DPS will increase. Also if you change the nature on 1st legend to “of the elements” or “of Death” you should increase DPS. Also could use Emerald to increase item quality on 1st legend to 25% which will affect DPS.
Here’s a link to the formula. This really helped me prioritize affixes.