Updating some things in the spreadsheets, decided to check on dnc (added geo buffs/debuffs, fixed Soul Voice bug).
Best direct DPS I can get on dnc vs Tojil is about 875. Compare this to 1100+ for mnk or drk, or 1200+ for sam.
On the other hand, dnc adds the following:
13% def down, which is pretty massive at the debuff levels being used (20% Dia, Angon, geo's Frailty). It's possible to get at least some of this effect from other jobs subbing dnc (eg: cor/dnc, drg/dnc), but is usually more awkward, not always sustainable, and in some cases reduces the job's native damage capabilities.
-24 evasion, and/or +7% crit rate (depending on whether you can keep 3 step effects going), both of which are fairly decent effects, and can impact how others gear.
10% JA haste for one party, which means DDs can drop to ~15%-20% gear haste, which may or may not be useful.
Now, putting a dnc in in place of another job with higher native DPS capabilities means it needs to generate sufficient indirect damage to make up that difference. Figure about 300 DPS split among the other 5 DDs means 60 DPS per DD.
13% def down can be 240 DPS (if not reaching cap). Maybe 40 DPS per step, aside from the first.
7% crit rate is about 25 DPS.
24 acc can be signficant, but assuming the DD is already capping with a bit of buffer, is more likely to only allow for maybe 10-20 DPS change in gear swaps.
In other words, it has the potential to contribute a combined direct+indirect amount of damage to match or exceed a stronger DD. Whether or not it can actually accomplish that depends on various other factors.
The downsides are lower HP, and figuring out where to put them within the limited DD slots (generally just 6 positions).
For Tojil, having 2 mnks per party for Mantra and Formless Strikes is usually a base requirement. One of the other DD slots is going to be the drg, which leaves just 1 spot for the remaining DD. That's usually allocated to drk or war to take advantage of the slashing weakness period, so dnc is pretty much left out. Shark is similar, though a bit less strict.
The bee is actually the one that would probably be the easiest to fit dnc in, given that it seems you want a variety of damage types being used. Rngs are good for piercing, and the boss fight goes fast with them, but tend to be much slower on the first 5 NMs. Setting up something like mnk/mnk (blunt, magic), drg/dnc (piercing), sam/war/drk (slashing) to balance things out would probably make the zone as a whole much easier.