I've been playing around with Zael a little. His Rally skill raises atk & matk for the whole party by 10%, well worth it in my opinion, even if it makes your characters constantly move out of position.
I really like his unique skills and the character artstyle. I will probably try to make him work, even if he might not be the most ideal member for the party. Supposedly his job 1 lvl 65 skill works much like the column skill for mages, as in if you pincer a horizontal row of enemies you can cover the whole screen with the attack. Haven't gotten his job 1 and job 2 lvl 65 skills yet, still a few levels short.
Sorry, but Sorman is probably the better option right now, Amina isn't really worth leveling. Sorman has a heal all spell that heals the whole party while Amina doesn't get that. The SS class makes also Amina rather slow to level up, I would suggest not using her.
Gegonago and his levitate skill will be vital for chapter 18, definitely level him.