Am I prepared enough to fight the superboss in Octopath Traveler 2?

Yesterday, I completed The Journey for the Dawn and defeated Vide in three attempts. I was about to do the Epilogue before remembering that there was an island south of The Lost Isle called ??? that I wanted to check out. I thought it would be some dungeon, but as I entered it I got the sense that it was something more important, especially with Al wounded there and with no enemies abound. I traversed up the staircase until I was asked to split my party in two.

I declined and looked up what was happening; apparently this was the domicile of a superboss named Galdera, which lives up to its name, being tremendously arduous to defeat.

My party is at a pretty high level; my lowest character is Osvald, who is at level 68. The other characters are not far ahead. For the record, Ochette is Thief, Thronè is Dancer, Castti is Cleric, Agnea is Inventor, Osvald is Conjurer, Temenos is Apothecary, Partitio is Arcanist, and Hikari is Armsmaster. Should anything be changed/are there any viable strategies to best prepare for this fight?