Maybe they could just make two versions of it.

You could choose which version to run, and the "story-mode" one would adjust mechanics according to whatever character types were in at the time.

For example, a DPS enters in Duty Finder. As he is a newbie, and he hasn't fiddled with any CHaracter Configuration overmuch, he had not disabled the option that will pop-up an additional window stating, "YOu can choose to run this in either Story-mode or Party-Mode." It will explain that Story-mode will open a queue for up to 8 players of ANY class that have unlocked it. It will change the boss mechanics if, say, 8 DPS registered, maybe for the boss to have high-health or invulnerability at certain stages and the DPS had to know when to pull back and charge up, but that he inflicted low enough damage that the "Role" techniques could protect anyone. If less than 8 characters had queued at the end of the timer, it would scale the enemies' strength accordingly.

It would be a long, complicated process, but it would eliminate the need to run it with a party that just wants to get through it, and it would give an option if you stubbornly wanted to party. When selecting "Party Option", it would warn you, "YOu will be unable to view cutscenes in this mode--please visit the Inn in any large City to view them afterwards."

It's work for the devs, yeah, but it's at least an attempt at a solution.