Just noticed a fun fact recently. Massacre
is probably the best 2-hand weapon enchant for hunters. Yet if we consider the item point value of the enchantment alone:
2 x Titanium Weapon Chain of dual-wielder
= 2 x 28 hit rating
= 56 hit rating
= 112 attack power (in term of item points)
> 110 attack power
= Massacre of 2-hander
If talking about gain in dps, 56 hit rating >> 110 AP.
Of course, this does not mean that you need to dual-wield all the time. For the same ilvl, a 2-hand weapon is usually slightly better in stats than the sum of two 1-hand weapons, so this probably balance out the weaker enchant.