Seedling

The fight doesn't last 18+ hours. The attempt lasted 18+ hours.

Pandemonium Warden can be defeated within 4-5 hours, but that requires intimate knowledge of the battle and that information is currently NOT available. If each wave would take 10-15 minutes to clear, the fight is still long, but doable.

Every expansion has had optional bosses that were hard to trigger and impossible to fight, until players deciphered the battle script and developed tactics for it.

Rise of the Zilart brought us Kirin. He's difficult, because he summons the other 4 gods. This fight is well documented and most linkshells can defeat this one in 90 seconds - 2 hours.

Chains of Promathia has Absolute Virtue. Trouble with this guy is it's massive regeneration and being able to use 13 of the player 2-hour abilities... We know how to counter the regeneration.. but despite a Dev video, we still don't know how to counter the use of 2hr abilities (in particular Benediction, which heals it back to full HP).

Treasures of Aht Urhgan offers us Pandemonium Warden. 20 waves of a boss+8 pets... each wave different, and many are very nasty indeed.

Perhaps the Warden isn't a fight a single linkshell can handle. Perhaps 10-15 minute per wave is undoable. Perhaps SE thought that linkshells could put aside their enmity towards each other and fight this guy in shifts... Too many questions are still left unanswered at this point to make a conclusion about the mental state of SE devs... (except for the ones that work on automaton AI.. those guys must be in a state of permanent inebriation...)