There's only a 60 dps difference between 359 and 372 onehanders, but let's look at your problem:
Simcraft 4.2.0 r1 shows:
372 BiS gear + heroic Lavaspines at 27.337 dps
same gear but 2x regular Lavaspines at 26.863 dps
same gear but heroic Lavaspine with agility instead of strength (mainhand) and regular Lavaspine offhand at 26.880 dps
same gear but 2x heroic Lavaspines with agility instead of strength at 26.728 dps
same gear but 2x regular Lavaspines with agility instead of strength at 26.233 dps
Conclusion? Weapon damage means almost nothing, strength is king. Even at worst case (2x 359 agility weapons) it's still only ~4% less dps to 2x 372 strength.