Berserker is serving me fine so far. I tried out using three Berserkers and one Black Mage and I didn't have any issues, it was just super boring. The fire-powered ship wasn't too much of a challenge, but it was the escape from Karnak Castle that really worried me. It's a tricky section with the 10-minute time limit, but I usually handle it fine, even getting all of the chests. And I was fine here... there were just some casualties. I did not bring enough potions, and used them all up. So then my only options for healing were i) letting people die and using phoenix downs or ii) using my elixirs. I ended up wasting like 6 phoenix downs. But I got every chest! Even Esuna, which will be entirely useless. Which reminds me, I'll have to go fight Shiva at some point. For fun. Moving on, job number three.
Ranger

Ranger might be useful, if I get a Dragoon or Samurai from the earth crystal, who would benefit from Rapid Fire. But as it stands, I have three basically incompatible jobs. Like, what abilities can transfer between them? I could pass Animals on to a Black Mage? I could get a Berserker that can Equip Bows? Not great. We'll just have to see what the next crystal brings.