This is just an assumption not a recommendation so please correct me if I made any mistakes, which I often do. This is theoretical and there are many assumptions in this text.
Regarding Glyph of Dark Soul, i can see it being actually useful for fights, in which we have to delay Dark Soul for more than 20s BUT the damage inbetween isn't unimportant.
From the top of my mind I can think of the
Spirit Kings (30% phase),
Elegon (Energy Charge phase),
Mel'jarak (Recklessness) and
Lei Shi (Get Away!)
Assumed having 4pt14 the overall gain of an unglyphed Dark Soul would be 30% * 20 / t and that of a glyphed one would be (27% * 20) + (3% * (t - 80)) / t with t being the time between the activations.
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If we now look at
Lei Shi both the Get Away! burst but also the sustained dps seems to be important.
The fight lasts at most 360s (6min hard Enrage).
(log mined data) There generally is a 52s gap inbetween two specials (Get Away! or Hide), there seem to never be two Get Away! in a row but there can be two or more Hide in a row.
Assumption: 50% chance of Hide after Hide or after the pull, 100% chance of Hide after Get Away!
If you use DS on the pull, you can't use DS if the first special is a Get Away!,
if the last special is no Get Away! you can use an additional DS 20s before the Enrage.
Therefore i see the following probabilities:
| DS on pull | no DS on pull
1 times DS: | 0 | 2
2 times DS: | 4 | 9
3 times DS: | 12 | 9
4 times DS: | 5 | 1
The overall increase of DS would then be:
| DS on pull | no DS on pull
glyphed: | 5,54% | 5,02%
unglyphed: | 5,08% | 4,05%
So to me it seems that generally using Glyph of Dark Soul for the Lei Shi encounter seems to be a significant DPS increase
IF it is necessary to delay Dark Soul for Get Away!
It also would be a DPS increase if you use DS on the pull but assuming DS is necessary on Get Away!, that's not preferable.
Note: The effect of Scary Fog is not taken into account.
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Now looking at another fight:
Spirit Kings, 196M HP each, assuming an average DPS 70k per player (6 heals, assuming tank doing also ~70k) * 19 = 1330k rDPS.
This would mean the first 30% phase would hit after about 100s (.7 * 196 / 1.33), the intervall after that would be about 150s (196 / 1.33).
The fight would maybe look something like this:
DS at pull - DS after 100s (first 30%) - DS after 150s (2nd 30%) - DS after 150s (3rd 30%) - DS after 80s (asap on the 4. King) - DS after 90s (as late as possible, this doesn't change anything without glyph but is a little gain with).
the overall gain now would be
unglyphed 6.10%
glyphed 6,36%
(~180dps difference)
With an average of 75k / 80k dps the overall gain would be
unglyphed 6,44% / 6,50%
glyphed 6,28% / 6,26%
So no real difference there. I'd probably chose the better burst over the minimal increase in the overall dps.
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Unfortunately I don't have enough data to go through any other fight.
What do you think of the Dark Soul glyph from this angle? Can you think of other fights, where the glyph could be useful?