Any job is bad if played wrong, but saying dnc is "bad enough" is flat-out retarded. As is his lumping them in as DDs.
I have another relevant question pertaining to the issue of slug shot pants.
I just discovered my relic pants have STR+3 and AGI+3, are those better than the +5 AGI of War Brais +1 for sure?
Also, Wood M Ledelsens vs. Rutter Sabatons. (STR-3 AGI+6 vs. STR+3)
I only ask because I'm unsure, I've been told STR is helpful for damage, but AGI is apparently the only direct modifier.
DNC needs no gear for Haste Samba. I guess they need to be able to hit the mob though.
I'm not sure it's fair to expect a random PuG DNC to do all that. I'd consider myself lucky to even get the Haste Samba, but I did do a disservice to DNC by underselling it like that. Very handy to have around.
However, they may still be more useful than a third DD. I had a DNC in my party at MMJSP once when I was on RDM. Party was:
RDM, 2x BRD, SAM, SAM, DNC
DNC wore full AF1 the entire party and did jack shit for healing. Just kept Samba up and had 5/5 merits. We pulled over 30k/hr. Honestly, that party was what made me most excited about Dancer. If such a retard could be so useful on the job, I was excited about how useful a good player could be.
If you do limbus at all, AF+1 feet are pretty rocking Slug shot and general ranged attack shoes. Pahluwan Pants are better than Relic for Slug if you have the MJSP Assault Points to burn, though Aurore will beat those out if you really need the acc 78+. I'd definitely attempt a few Nyzul boss runs for Denali legs for Quick draw at some point. They destroy most of the alternatives, and are fairly easy to get if the group you find can clear up to the boss (As in, no one else wants them aside from other Cors or your occasional retarded NIN Nuker).
I'd avoid the Corsair Bullets, though. With Martial Gun and sushi you really rarely need the accuracy bad enough to justify the loss in base damage over Steels. If your acc is that bad, you'll get a lot more swapping other slots long before you come anywhere near throwing out 13 damage in the ammo slot. If your acc ever gets to be that horrid, you should switch to Detonator with Martial or, in a more extreme case, Leaden Salute with Peacemaker anyways. There's really no reason to waste the time doing the ENM for the bullets unless you're levels 61-65 (And you're not, since Joyeuse is 70).
Worse comes to worse acc-wise and you're completely out of other options (Other WS not unlocked, etc etc), you can always /RNG for the extra acc and sharpshot (I'm assuming you were /War or /Nin before). Sushi + /Rng is going to absolutely overload you on acc for most older content (or should, gear-dependent), but Abyssea mobs are notoriously evasive and I'm sure you'd rather hit for slightly less than not hit at all.
yes
Aurore Gloves vs. Commodore Gants for Slug Shot?
STR+4 / AGI+4 vs. AGI+2 Ranged Acc+5 Enhances Snapshot
Coffinmaker is a Martial Gun with less accurate Slug Shots, less damaging (read: unusable) Detonators, and +9 R.Acc for TP phase shooting (read: pointless since you're using Joyeuse), that costs money just to make not worthless. The 1 DMG bonus Coffinmaker has over Martial Gun is the only thing it has going for it, and the +9 R.Acc pales in comparison to the accuracy bonus given to Slug Shot. All the old tests that said "+40 Accuracy" at 200% TP are probably bunk, but its definitely a much higher number than +9.
Just allowing Detonator to not suck is reason enough for Martial to beat Coffinmaker, letting you have a reliable WS against high evasion targets besides Leaden Salute. Its also the best gun for Leaden Salute by far.
tldr: Martial Gun + Steel/Oberon's is your general purpose gun/bullet combo. Martial Guns are getting real cheap too. Note: I haven't really given Magian guns a look yet.