To Spuffin,

You must level a job to 50, especially a Disciple of War, for the following reasons:

1) AP to use all of the abilities you got from other classes as well as the level II weapon skills from the 50 class.
2) Ability to hit NMs.
3) To not get killed in one shot by NMs.

My Archer is 22 right now. You are correct by saying I can use Cure II, Siphon MP, Raise, Feint, Second Wind, Bloodbath (true in my case). However I would not have much room for any Archer abilities at this point. Instead I assign Archer buffs and weapon skills, and maybe one or two abilities from other classes (Cure II and Invigorate). To do what you are saying would require I attain a high rank on Archer. Even then, I would want the relevant break skills for NMs, and would be too busy trying to build TP to do much else.

Also recall that on Archer my spells will all be single target and weak. Invigorate is on a longer cooldown and also weaker. If I were to level Lancer to a high rank for Invigorate II, then honestly I feel I deserve to use it for all the hours I would have put in toward it.