The Single Most powerful *thing* in FFXIV?

[HiraishinNoJutsu]

The game has a lot of encounters whether they be canonical in lore or Fanfictions made up by a wandering minstrel I pose the question

"What is the most devastating attack/spell/attack ever used in the game"

The Ultimate Crossover from Elidibus, "UNLEASH ULTIMA", or Is it just a straight up the "Sundering Kick"?

Power Scaling is cool in any game and I am curious if we ever got an explanation of what Thing that we have seen is the most powerful? What was the most impressive feat. WoL has done? etc.

Edit: Fun Question to also ask "If every boss was put in a gauntlet and we had to crown the most powerful of them all, who would you bet on?"