So, seeing as that fight is a horrible one to theorycraft, I looked a bit further back in your guild's logs. Specifically to your Feng kill from Dec 19th.
The majority of the issues I'm seeing here are likely carrying over to the fight you linked, but are much easier to spot here.
Also remember that shadow excel's in excute range, if you dont get to execute range before the wipe, your dps will be lower. Not much you can do about that. It'll likely raise you 5-7% overall by making it through execute.
1. Uptime. Your SWP and VT uptimes are patchy at best. You've got gaps sometimes 10-15 seconds long where you didn't have DoT's up.
2. Talent choices, as you mentioned yourself, DI and FDCL. Its bad, only time its really acceptable is when you're moving close to the entire fight, as it allows you to get a lot more instant casts. If you're standing anything remotely close to still you'll want MindBender and DI instead. Looks like you're getting overwhelmed with procs to the point where its affecting your uptime. Sub 20% on Feng, you had maybe 50% uptime on VT.
3. Mind Blast. You're missing a good amount of opportunities to cast it, Over a 6:56 fight like your Feng Kill was, you should've gotten 44 by just casting it on cooldown, With DI that should go up a solid amount, you had 46. Leaving some room (assuming Divine Insight procs mid way through the cooldown every time, you could've gotten almost 55.
4. Devouring Plague. About half your Devouring Plague casts were when you only had 2 orbs, as opposed to the full 3. Its worth considerably more to wait for the full 3 orbs before using up the GCD.
Your gemming is a bit funky. You have reached haste plateau, but you're using a mixture of hybrid and pure gems, Drop the pure haste gems, and use Reckless in all yellow sockets, purified in blue (only if the socket bonus is worth it) Generally most sockets will be, the closest I've found to not actually gemming for color was a 60 crit socket. Anything with an int socket bonus, or secondary stat greater than 80 points per gem will be.
As for attenuation movement that you mentioned, yes spamming SWP is the best option, You'll get a few extra proc chances. Make sure you go into that phase with VT at full duration, (refresh it as soon as you see that ability used, doesn't matter how long you have left) By spamming SWP, you'll get the opening tick which can proc and reset the duration, Seems to be a 25-30% increase in tick count during that time, just from what I've tested, I could be wrong on that. You'll likely get 2-3 DI procs during this phase. Mind Bender is also valuable to use here. As are Halo and Divine Star. Sub 20% you'll also be able to weave double SW
's into the SWP spam. And hopefully with that a few Devouring Plagues.