Here's my experience.
I'm a 75 dnc, with fully merited sword, and Suppa. This gives me just barely a C rating in sword. Here's the deal, the trick with using a joyeuse effectively is going /sam. Dnc/sam gains TP unbelievably fast. I easily out gain a sam, or anyone in haste gear aside from "maybe" a thf dual wielding the fastest daggers they can get.
As for gear, you do not need to sacrifice haste/stp gear for acc. I personally use the cobra unit gear that can be gotten from campaign. This stuff is marvelous for dnc, as if it was made just for the job. Acc, stp, and -enmity. I currently have +45 acc on gear alone, + 13 stp, and as /sam that totals for an extra 2.8% tp per attack round. I do not atm have rajas ring, or brutal earring, but I do wear the Walahra turban for headgear, SH for body. I would use enkidu, or antares harness preferably, but they're more or less just an upgraded SH. After I get my Rajas Ring, and Brutal earring I will have 3.4% more tp per attack round.
I main hand my joyeuse as /sam. With all the stp, and the DA rate of joyeuse which as far as I can tell is 45-50%, and according to the other testing data I've read it is, I get between 7-15% tp per attack round, and this is with my delay being a little less then half of that of a dnc/nin in haste gear, with suppanomimi. I easily out tp gain a dnc/nin, to the point where it's embarrassing. I do on occassion go dnc/nin, but that is limited to the periods when I don't have anyone to heal in a campaign battle. Tp gain as dnc/nin, main handing a dagger, off handing Joyeuse, is 10-15% tops, but again that's at almost twice the delay of /sam and just the joyeuse. The delay on most of the higher lvl daggers can use is the same, or just a smidge less then Joyeuse.
Now the question you may be thinking is this. Ok, you mentioned campaign, but campaign mobs are gawdawfully easy to hit at 75, but what about NMs or meripos?
Meripos are easy as pie. One of the biggest advantages is having meditate to give yourself a nice tp kickstart. Against Greater Colibri, or mamool, I have NO need for sushi. Do I use it? Yes. I use Tuna sushi because, yes it does help with acc, but also for the nice hefty CHR boost it gives, which helps my heals. I frequently main heal for my LS merit pts, usually consisting of 5, yes count em, 5 DD jobs and just me healing, with everyone being either /nin or /sam. Step acc with the AF gloves is more then enough to keep steps on. I will say, yes...I do see an acc difference between daggers, but the DA on joyeuse makes up for it, as well as Zanshin from /sam. I also wear Bushido Cape which enchances zanshin, and zanshin CAN proc on both swings on a DA attack round.
I've toyed around with both /nin and /sam enough that I will forever HATE going /nin unless I know there will be an AOE problem froms mobs that shadows can block, or if I solo in campaign and want to actually use my WS. Otherwise, go /sam and use a joyeuse.
Edit* Currently I have 1 step acc merit, 1 haste samba merit, and 5 Reverse Flourish merit. Even with just 1 step acc merit I see a significant difference.
Edit again* >.> Also, if I currently had an Azoth, I would probably go /nin more often, just because that dagger is really f***ing cool.
Also, I have personally tested this out myself with a ton of borrowed haste gear from my LS, /sam and wearing the cobra stuff with all the store tp is MUCH better at gaining tp then tons of haste. Do remember that haste lowers the tp you gain, but Haste Samba does not effect this specifically. Dnc/nin decked in haste gear just can not compete with /sam and stp gear using a joyeuse. If they were using just a dagger, it MIGHT be different, but from my testing like that, it's not much slower then /nin and dual wield
