Originally Posted by
Totaltotemic
It's because someone somewhere calculated the cooldown reduction incorrectly (as a factor of reducing the cooldown by that percent instead of using the formula for haste that it actually uses) and came up with a number that the energy from the reduced EB cooldown was worth. Since then, people have been slapping it on BiS lists and coining for it without an actual understanding of how the trinket is supposed to benefit WW.
The actual math surrounding the trinket is that the 553 ilvl version reduced EB's cooldown to 43.2 seconds, which is worth 16.8 extra energy per minute, or the amount of energy you would get from 1190 haste (but not the effects from haste like increased attack speed or cloak/meta RPPM), which is roughly equivalent to ~700 actual haste (around 60% of the value seeing as it doesn't affect about 40% of your damage). Compare that 700 haste to the 1959 mastery on the TED (which in itself is less than what Haromm's gives in terms of DPS) with essentially equal procs, and you have to figure that the FoF cooldown reduction would have to be worth at least 1200 rating, which is nearly impossible as 1200 crit rating at 50% crit would be a ~1.4% DPS increase and using FoF that much more is nearly impossible without significantly devaluing your own haste and mastery, as well as both T15 and T16 tier bonuses.
So no, AoC isn't good, but a lot of people think it is without a solid reason and it's pretty hard to unring that bell.