They represent different jobs



Tank, healer and caster were confirmed in the live letter.

Far left is using MNK weapons sheathed on the side.

DRG is my own assumption as DRG usually gets a "lite" version of tank gear.

NIN was labeled as "melee" in the live stream but since we already found MNK and possibly DRG only NIN remains.

And by elimination the lala would be BRD/MCH.