Using consolidated log information from a number of users, I discovered an issue a few days ago which some of you might have seen reported on forums and Twitter.
As we know, Draught is on the GCD now, and like any GCD can't be activated until the previous GCD is over. Normal abilities can be queued ahead of time, allowing you to play slightly ahead of the GCD to mitigate downtime caused by latency (see: custom lag tolerance). However, items cannot, leaving you at the mercy of your latency, creating a delay between abilities cast immediately before and after Draught of Souls.
Being unable to queue Draught means you have to wait until the server has acknowledged that your previous action is completed and its GCD is up before the game will allow you to use the trinket on your end, which then requires your client to send that information back to the server saying you're using the item and wait for it to return a confirmation. The whole round trip typically eats anywhere from 100-200ms, plus or minus a few dozen depending on your latency. This happens both before using Draught, and before the next GCD following Draught as well, creating a total of ~200-400ms (0.2-0.4s) of wasted time during Battle Cry.
Unfortunately this is an engineering issue, so it's extremely unlikely to be changed, and simply something you have to live with. I've already had a new version of SimC uploaded which replicates these delays, which is why some of you might have noticed that downloading one of the newest builds resulted in a seemingly random loss of ~20k dps with the trinket. Despite this, it's still the best single target trinket for Fury, just not by as large of a margin as before.
TLDR:
- There's a 100-200ms delay before and after activating Draught of Souls.
- There's nothing you can do about it.
- It's still the best trinket.
- SimC accounts for it.
For more information on how to correctly use Draught of Souls, see the Arms and Fury guides pinned at the top of this forum.