Yeah, I'd have to say at least for this particular fight tankspot kind of glosses over some of the finer points. We had the exact same problem with blood council in both 10 and 25 when we first started exploring it, and it took some rather off the wall "hey this is going to sound crazy but what if we..." thinking to come up with something that works.
Something that can help your raid identify this kind of issue is to use live log parsing to WOL and/or addons like GrimReaper to track the overall timeline of who takes damage from what and when. When we started out we did it by the tankspot book too and couldn't figure out why it seemed like the keleseth tank would occasionally just implode; at first we thought they weren't picking up nuclei, but once we had several dozen attempts under our belts (over the course of a few weeks with a few rough successes and a few wipefests), several of us had become comfortable enough with our roles that we could actively watch the keleseth tank and really narrow down the cause of the issue, which eventually led us to the idea to drop shadow resistance, and then it was just a matter of mathematics and realizing that taking 18k+~6k damage every 2 seconds is a lot scarier with only 25~30k health than it is with 50~60k.
XI Wiki


