You are correct situationally Dragon's Breath can be very good. I especially agree on the IR Yut Encounter. Wolfpack rounds can be mitigated by mobs in the room but dragons breath can get the job done, this of course assume she has started singing. I do keep Dragon's Breath around for these instance. I do disagree with you though Dragon's Breath is not better than I think because I would only pull it out in a niche situation meaning it sits on the sidelines the most of the time. I don't really agree with the idea of using it to clear thralls, most of the time they are mitigated by a variety of different strategies. Even in comparison a weapon like Gjallahorn will kill the thralls with a blast and then the wolfpack rounds will hunt down the other close thralls giving your team breathing room. I have never personally seen the solar flare as an effective deterrant. The biggest problem with dragon's breath is the solar burn makes enemies move. This really hurts it for boss fights making it really only viable on super immobile targets like you point out. Bottom line I use my heavy weapon when I either need to kill mobs as fast as possible or on boss fights. Dragon's Breath doesn't fit with my playstyle for the majority of these encounters.