Sure its good for old area's, though try to fight solo versus a bird in the outer regions and watch you stand there for 10 seconds with your great sword while you miss, while you use Lunge and do 1000+ damage and you're dead.
Support job Red Mage, sure good for curing once mp runs out monster still has 75% health left, this job is not very support friendly, its good for blocking magic basically that's it.
You wanna duel wield swords, sure sub dancer or ninja rely on Regen IV or Ninja shadows.
Down fall, monsters hit too hard curing waltz is okay but wont save your life 50/50 chance, shadows well you're giving up cure IV for just Regen and your auto regen ability, once monster does Aoe or a move that wipes your shadows you basically are dead and these monsters tend to use TP moves faster because their accuracy is like 95% and a 5% miss rate.
SE wants you to have a Mage partner well news flash usually nobody wants to do the same things as you do.
I do see potential in Rune if they were to give it a Cure IV spell which would allow Support jobs be useful.