frankly, my DPS is crap
Should I be using Mindbender? If so, should I be using it immediately off-cooldown or waiting til 5-10 stacks of VF? Or should I be using Lingering Insanity instead?
i have logs but can’t link them here apparently. but i should be searchable on warcraftlogs
If the fight is less than 3 minutes its best to time it with lust. Over 3 minutes you use during voidform usually early on. Use the LI talent.
In the grand scheme of things your low dps is due to poor gear and not having the best azerite traits. Also check your rotation. It seemed like you are not in void form as much as possible. About 15%-20% less than average.
I am using AzeritePowerWeights addon and Bloodmallet to choose my traits - which do you think are incorrect?
WCL gives you the optimal traits for fights. You can see what the top shadow priests are using for each boss. We dont have much variation for this tier. Other sites might help you min-max between other traits. Mostly your goal will be to get 3 SA 2 COI and 1 whispers or 3 COI 2 SA and 1 whispers. SA is top damage right now. Its basically like the damage you would lose not casting mind blast the whole fight. Thats how much you are missing out on.
This is SOOO helpful, thank you 
Mindbender is only really worth it with dark ascension right now imo. I would highly reccomend taking lingering insanity because not only does it make your rotation and general gameplay feel smoother but it also reduces the amount of haste you would want to stack increasing the value of crit. And stacking more crit means more synergy with SA.