Gear
1. Your helm should have a 40 Int gem in it, the socket bonus isn't worth the loss of 20 Int.
2. Jaws of Defeat is a poor dps trinket, sure the Int is nice but with no proc it makes it very lacklusture. Something very attainable that would instantly be better is the moonwell chalice but given the new tier there might be something better again to get. I think you can farm a decent trinket from the new 5mans.
3. You have the offset t12 shoulders which is depriving you for the 4pc bonus which is very tasty and as such you may not reach the dps level you want.
Reforging
I'm of the belief we should hit cap, particulary if you feel you are struggling with your dps because it just makes life easier if you don't have to react to occasional misses. You can hit cap by making the following reforge changes.
Helm: spirit -> mastery
Shoulders: spirit -> mastery
Gloves: restore
Ring1 (Soothing Brimstone Circle): crit -> haste
Ring2 (Signet of the Twilight Prophet): restore
Wand: restore
Enchants
For your level of haste it's my belief that 50 haste rating to gloves is better than 65 mastery. You can look at Kilee's work on how stats behave at various levels. This is a very minor thing and while my opinion is to change it to haste you can form the other opinion if you wish.
Log Analysis
1. DP uptime is a tad low, SW:P & VT were >= 98% but DP was only 94%. I'd suggest that it may have dropped off when you had to exit the twilight realm for that encounter. The idea is to ensure your dots are maintained by refreshing them early if you do need to leave the twilight realm.
2. You averaged a MB every 9.4 sec but the CD on MB is 6.5 sec (talented), You really need to get more MBs in and have the average number of MBs around the 7 to 7.5 sec mark.
3. You have 3 x SW
casts and due to the fact they only hit for 6K each you must have casted this when the boss was > 25K health which you should never do. Are you doing this for mana? I wouldn't have thought you should have needed to do that. Did the boss get to below 25% health at any stage coz if it did you didn't utilise this spell when you should have.
4. I'm not sure how accurate the log is, but shadow fiend was only up for 14 sec for the encounter. I'd imagine this is only half the possible time, or is the fiend dying to the aoe damage?
Intangibles
How you use your cooldowns in important. Are you simply using dark angel on cooldown or are you timing it to co-incide with other temp buffs like volcanic destruction? Are you ensuring you have a dark angel when you are utilising bloodlust/heroism?
For progression raiding, particularly for dps gear checks, you should be utilising all the consumables you can. I don't see any volcanic pots in your log. You can pre-pot a second before the encounter starts and utilise another during bloodlust. Go craft/purchase some asap.
For this encounter, are you jumping out of the twlight realm as late as possible? When you do it, you lose contact time on the boss... so the idea is to jump out as late as possible without being risky. Ensure your UI is allowing you to do this easily, you might want to look at binding the extra action button 1 so you don't need to click it.
You're not doing a lot wrong, keep at it.