So I put some insight in this thread into practice yesterday. I ran Delta 1.0 a few times using Blizzard IV during every Umbral rotation, my last run ended at 3.8k.

Conversely, I ran it a few more times, this time only using Blizzard IV when Convert was ready for the 8 Fire IV rotation. I cast it a total of three times in the entire fight. My number ended at 4.3k on the final run.

I almost feel like this is the intended way to play BLM, because after I broke the habit of casting it every time, it just feels so much smoother. I'm not complaining whatsoever. The Umbral Heart trait is aoe-related after all, who says it has to be a part of our single target rotation?