So far most of the steps in the legendary quest line have been pretty cool. The gem for the sha touched weapon as well as the eye of the black prince were pretty cool but nothing amazingly special but since they were just the first two steps the nice little bonuses they provided were pretty cool. Then the legendary meta came out and omgawesome. Huge dps increase and an amazing contribution to your arsenal. Same thing with the epic cloak. The ilv increase is just amazing and it brings a really high amount of dps especially since it doesn't have any stats like hit/exp (which most rogues are overflowing in) and is all damage.
Now the legendary cloak doesn't get any ilv increase. Doesn't get any stat budget increase just gets a spiffy little proc and some particle effects. In SoO gear assassination rogues could very well have ~50k ap or so with combat having a lot more but for ease of math lets just say that an assassination rogue is sitting at 50k ap. The cloak hits everything in front of you (I'm assuming it's every .5 seconds and not ever 5 seconds for 3 seconds and is just a typo atm) for 1+20% ap which means it hits with 50k ap is 60k damage when it procs but it only has a proc rate of 1.5 ppm which means that the legendary cloak... the end item of this expansion... the amazing thing that everyone has been waiting for will give all of a ~1500 dps upgrade single target. I'm thinking that most pieces of gear going form ToT lvel to SoO are going to give higher dps upgrades than that. Granted if it procs on an aoe pack it'll be amazing (think of those mass aoe packs in HoF before the first boss... would be seriously an insane proc there) but since it'll only proc less than 2 times a minute and most of the time rogues are single target the vast majority of our awesome cloak is going to be a very small upgrade. Hell the legendary meta hits for around that much and procs ~20 times a minute... It seems like they balanced the proc around it's aoe component rather than single target which makes it over all kinda bunk.
I dunno. For the grand finale of the legendary quest line instead of an amazing display of fireworks it seems like they're ending on a bottle rocket.