Cheaper and Easiser to make ammo?

[Malacite]

Not sure why you chose ninja in your example. Additional tool cost is as close as any other job gets to an additional ammo cost.

Universal Tool Bags are incredibly cheap from Port Bastok, and save a tonne of inventory space.

And some ninja use shuriken.

Name one. Only an idiot would even bother with them at this point. Shuriken used to have the highest DPS of any weapon in the game, but ever since the caps went up that's gone right out the window. So there's really no justifying the cost of them whatsoever at this stage in the game.

It would be wonderful if we got more (cheaper) synergy recipes for ammunition, and I mean all types - Arrows, Bolts, Bullets & even Shuriken (along with a new higher level shuriken to replace Fuma) as it's much easier to HQ during Synergy than it is Synthesis. Ignoring the multitude of other balance issues facing RNG, it is rather unfair that jobs like WAR & MNK can absolutely destroy RNG now in damage, for free, unless said RNG has a Gandiva and even then it's still pretty close thanks to Haste.