"Why?"
Atlan's first mission had more variety in their team's composition. They had one tank, one archer, one pugilist, a stun wizard, and a scout. He would have thought that a high-ranking team like them would be like that too.
"It's because we're fighting an Infection Canzer. Our main challenge in this mission is not to get overwhelmed by the number of Ifrit Canzers that come towards us.
A DPS is extremely unsuited for this kind of job. That's why none of them joined this mission. They can do tremendous amounts of damage, but only to a single target or a small group of them. They'll be useless against an Ifrit.
What we do need are Tanks and Mages. Mages might not have the greatest destruction power, but they can spread it out to a large area. That would work extremely well against Infection Canzers who are weak, but numerous. Tanks, on the other hand, can absorb the damage the Ifrits inflict on us and protect the backline.