It does seem pretty unfitting, depending on the boss and setting. First and second bosses of the level 73 dungeon and Grand Cosmos probably could have just kept what they originally had (A Fine Death, I think it was? Alternatively, if he could/were allowed to, Soken could have given those dungeon bosses the theme 'Reign of Pain,' Shantotto's theme. Definitely would fit well in Grand Cosmos). Amaurot could have had Phantoms on the Lake or Nemesis and Twinning Tumbling Down or Shattered.

I dunno. I don't mind the theme, but it definitely doesn't fit for some fights. High Treason and Paradisaical Predicaments could have worked, too.
One good thing I will say though is that at least Persistence is gone. I hate that boss theme the most in FFXIV and wish it would stop being used.