I beat it maybe a week ago, with all characters at level 50 and probably about 90% of each one's license board completed. Though I buffed everyone up for the final series of fights, I didn't have to switch anyone out. At one point, I intended to do all the sidequests (a.k.a. hunts) but only got 24 marks...running around killing one monster at a time gets old. I just wanted to beat the thing and be done with it.