It is beyond why people would go for Swelling Shadows. The proc has a 4.5 sec cooldown, so increasing the chance to 65% from 50% with 2 points is just useless given the small increase it gives due to the long cooldown (for a proc).
For the rest, wither can also be a great for utility (since it hits 5 people, instead of 3 of DF) and with the talent that increases it's damage with 30% you get the same DPS or more compared to DF. It also gives up to five enemies a damage debuff and slower movement, which can be extremely useful in Warzones.
I would run this build instead:
http://www.torhead.com/skill-calc#200rIMszMskbsZbZf0c.2
The points in Dark Embrace can also be put in Torment, depends on what you like most.