I noticed, both by practicing on a dummy and running SimCraft, that the 4-set bonus far outweighed the 567 Darkfallen Shoulderplates (no, iLvl is NOT everything). But when I equiped them and ran the simulaion, I got this surprise:
MH DPS 7.32
OH DPS 3.65
First, discard the dummy results completely. In no way does it emulate realistic raid conditions. No movement and no AMS soaking would artificially inflate Haste's value by a lot.
I assume that your Simcraft profile matches your gear and glyphs from the armoury. I note one important fact on your armoury that is contributing to your high Haste value: You are not using Plague Leech. This talent devalues Haste by quite a bit, and is essential because it is a much higher DPS gain than Unholy Blight. I would advise switching to it immediately.
Moving on, you want to ensure that your sim utilises the following:
-AMS soaking (it usually does, but double check)
-Accounting for higher AMS uptime due to the Evil Eye of Galakras trinket, and the Regenerative Magic glyph
-Plague Leech, assuming you take it (and you really should)
-Movement (Patchwerk fights aren't going to give you realistic stat weights)