In typical video game conventions since the days of old, the final boss is, nearly all of the time, the most challenging boss of the campaign for obvious reasons. In Stormblood, The Royal Menagerie, being the final boss, also happens to be the hardest boss of the MSQ. So in other words, Stormblood is just following standard video game conventions, like most other games, new or old. What exactly is the problem here, again?

The final boss doesn't need to be nerfed, nor should it. After the curbstomping that is Ultima and King Thordan, The Royal Menagerie is the first FF14 final boss that truly felt like a real final boss battle to me. If you're having trouble, learn the mechanics of the fight and practice. If you don't understand what "mechanics" are to begin with, spam Bardam's Mettle over and over again until you can clear the second trial comfortably. If you keep failing even that, well, what else can I say but "git gud?"