Altar of Fangs

I checked this before writing anything above, because the report prints the same word in two different sections. From the log's own spell table and the tool's registry:

  32645     Envenom   Assass Rogue's Assassination Rogue finisher -- not an enemy spell at all
  1289416   Envenom   the enemy cast, registered interruptible
  1307571   Envenom   the debuff it applies, registered dispellable

So "Envenom 29 of 98 leaked" in the interrupt section and "Envenom 20x left up, 12,033,622" in the dispel section are two different spell ids describing the two ends of one problem, and neither is your rogue's ability. Arbiter is keying on ids correctly. This note exists because a reader looking at two Envenom lines has no way to know that from the page.

  pull 7  at 15:26  cost 0:45  0:22 fighting   0 enemies  3 deaths  11,537,358 taken  50% kicked
  pull 8  at 15:57  cost 0:30  1:08 fighting   6 enemies  2 deaths  17,401,973 taken  62% kicked

Pull 7 killed nothing at all and cost three lives. The group's interrupt rate across the whole key was 78%; on the pull that wiped it was 50%, and on the recovery pull 62%. Both well below the key's own average -- and Envenom is what was getting through, 29 of its 98 casts unstopped.

That is the causal chain in one line. A cast that is not interrupted becomes a debuff that has to be dispelled; a dispel cooldown already fully spent cannot take it; the debuff runs its full duration and does 12 million damage. You were saturated at the last link. The slack is at the first.

At 15:42 Envenom killed you: 1,537,287 damage over 12.4 seconds, 735,190 healing received. Enh Shaman died at 15:43, Devourer DH at 15:43.

Two seconds before your own death you cast Lay on Hands on Devourer DH. I checked the cast list to be sure that was one press and not two -- you used Lay on Hands four times in the key, at 5:59 on Assass Rogue, 15:40 on Devourer DH, 22:52 on Enh Shaman and 30:08 on Assass Rogue. So the "own cooldowns: Lay on Hands" line in your death window is real but slightly misleading: that button was spent on somebody else while you were dying, not on yourself. Devourer DH died anyway seconds later.

Nothing in the record suggests you should have saved it. Four uses of a long cooldown in a 33-minute key is using it, not hoarding it.

Mechanics 90 -- the only sub-100 mechanics score of the night -- from 1,691,270 damage that comparable players did not take:

  Messy Eater      x5    (peers 2)
  Deadly Venom     x13   (peers 4)
  Bloodletting     x3    (peers 1)

These are worth taking seriously precisely because the peer counts are not zero. A "(peers 0)" line is usually an artifact of how the comparison group was cut, but here real teammates sat in the same cohort and caught these fewer times than you did. Deadly Venom at 13 against a peer figure of 4 is the one to look at.

It cost about 1.4 points of the final grade. A small finding, reported as a small one.