The devs said if anything assassination might receive a buff down the road for its Aoe.
Shadow priest 6K above you with 17 ilvls more, Ret has 8, Mage 3, hunter 7. The only one in there that seems "off base" would be the arcane-mage turret. Just saying. When people have this wildly swinging item levels, a simple "he did more DPS, his class is OP" doesn't really cut it.