Characters being unable to kill much even if all their skills trigger is definitely something I'm concerned about. It's one reason why I'm hesitant on bringing Samatha back into the quest even though her elemental attacks really help with taking down Mithra's shield. Elemental damage is just so weak in the entire event.
Out of the 4 or 5 runs I've made through the event so far, I can safely say that Battle 1 isn't a huge problem. Even with a poorly prepared party, just Korin and Bahl doing a pincer on Calista is able to take her down in 2 turns. With more DPS and positioning I might be able to take her out in 1 turn, but I'm not counting on it lol. I've also had pretty good luck on Battle 4 without a ton of planning. 3-4 turns max, as long as I don't get fucked completely from stupid positioning at the end of Battle 3.
The most frustrating thing about aiming for Perfect Fate is that without an accurate way of calculating how much movement time I'm accumulating, I don't actually know where I wasted the most time in my runs. I suspect the last two battles, but it would be better if the quest had a sort of extra bar at the top or bottom which drains as you move, like in Puppet Show. Some sort of indicator would be nice.