TAJA gives you 80% of damage. That ammount of damage is significantly big to be ignored. Maybe in Ranger the situation is different since that class receives a lot of % skills in ranged attacks, but in Hunter, and unless you have too much time to lvl up until lvl 150 (And even JA Bonus is just 20%, which is just a supplementary skill, especially for FO since JA Bonus and Tech Advance unlocks Tech JA Bonus), you really need TAJA.

I can confirm it because there is a certain point that you'll deal bosses with no element weakness, which is a huge problem if you don't have access to that skill. Furthermore, in time limited quests, the worst thing that you can do in that game is lacking of damage, and I'm talking about taking risks for dealing damage with Fang Rush or Meteor Crush, the two GAs that Altiea mentioned.

One of the things that I do for dealing that damage with TAJA with the same GA is putting Technic Usage, which allows you using techs. You don't need offensive techs since you'll lose GP dealing 1 damage to the enemies. Instead, you need at least start your GA combo with Shifta/Deband/Resta/Anti depending of the situation of the quest, and then using the GA that you want.

Furthermore, Shifta and Deband are much better than in PSO2, and there is a difference between using your GAs with Shifta than using your GAs without it.