Definitely a possibility; I had to use Hymn of Hope about halfway through the fight, then used Divine Hymn at the very end, but even still, that's only ~17 seconds if I'm doing it perfectly, which isn't anywhere near 10%.
Again, I'd like to say it's because of the hymns and waiting for SFiend to be up to pop AA, but I can't be positive. It's something to watch for, certainly.
Not sure what the numbers should be like on Ultraxion with MS/MB rotations on the same target, but I had thought I had applied it every time and let the full durations tick, only ignoring a refresh if within ~2 seconds of an AA/SFiend MS/MB rotation.
From what I’ve read, I shouldn’t be saving MB for three orbs every time, but rather, using it on CD. As for MS, I only used it in preparation for MB during AA/SFiend, but if I’m wrong in doing that (I cast mine spike repeatedly until MB comes off CD, so sometimes it’s 3-4 MS for every MB during that rotation), it’s certainly something I should look into. Typically, I've found that I can go MB -> MSx3 -> SWD -> MB and waste no orbs. I skip a MS on the last set of the rotation so that the final 3 orbs from SFiend will be used for MB rather than MS.
Even though you're talking about your offspec, I appreciate your thorough examinations and insights.
Edit: Also, looking more in depth at the archangel uptime (54 seconds), it adds up almost perfectly with my SW:P and DP timers (4:29) to add up to 5:23 (compared to the total fight time of 5:33, and I start the fight with AA/SF, so my DoTs don't start for a while initially). No real idea what happened to my terrible Vampiric Touch uptime (3:35? wtf?), so that's probably 100% fail on my part. Also, sub 25%, I prioritize SWD over MB because I can move around while spamming that button twice to force-proc apparitions.