I'm missing you on one specific point here.
It uses exuviation at exactly the same rate using just BRD debuffs.
The only difference is it doesn't heal itself with it. I understand your point about it refusing to use the ability though. That would be the core reason behind not doing it. My observation was that it did not give any issue whatsoever in that regard though. We had 2 BRD casting Threnody, Elegy, the Addle song (the name escapes me, it's 1am) and Requiem on it the entire time.
For finality's sake, a few timed kills:
Kill 1, all debuffs. We decided to start killing it after about 1 minute and 40 seconds. From that point it took about 3 minutes and 15 seconds to die. That makes the total fight 4 minutes and 55 seconds.
Kill 2, only BRD debuffs. We were DDing the entire time, it used Exuviation for the 20th time at around 2 minutes and 10 seconds (we started Kill #1 at around 14-15) and was already at 60%. It died 1 minute and 50 seconds later, making the total kill time 4 minutes.
tl;dr if you're really strong you save about a minute. It's totally inconsequential, but still a fun little trick.
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