Oh, I see... Guess my theory was shot then.
Makes sense too, since at level 13, the offhand weapon bonus catches up to the main hand at +25% damage. Weird, though, is that there's an Ego Draconis walkthrough that mentions leveling Dual Wield Expertise to level 15 and having the offhand weapon do MORE damage than the main hand (and he was pretty accurate in everything else, so it's pretty odd that he got this one wrong).
Thanks for welcoming me and for the quick reply!