Except it's not, able to cap steps faster is DPS increase for the job itself, and every other DD job in the pt. It doesn't matter if it's annoying, it seems like a DPS gain for the job to me. If you find using JA annoying in FFXI, MNK or SAM is the job for you.
I really would like to think you're familiar enough with this game to know that spamming JAs every 5 seconds is not going to be helping DNC's output, DEF Down or not (and they need to continue using the steps every so often to keep the daze up). The idea that it would help a group is worth nothing too, because nobody is going to get a DNC to be doing DEF Down, they'll just get a GEO if they want that.

The thing about utility for the light armor jobs (NIN, THF, and DNC) is that I wouldn't have a problem with that meaning they have weaker damage output compared to heavy jobs if they could actually figure out what the heck they're doing with this utility. They need to:
-Make DNC's heals and debuffs better and make them better DPS
-Make NINs be able to tank something actually worth a damn, or just give up on trying to make them tanks because they're doing a really bad job at it
-Make THF at least the best DPS of these three because they have the least versatility out of them

I'm not sure about Byrth's claim that NIN is currently a better DPS than DNC, though. I mean, when both of them are all hasted up and just TP spamming I imagine katanas outpace daggers, but currently the place these jobs shine is in trash farmed solo content or whatever, and I'm guessing DNC can do better damage than NIN by self-skillchaining. Not saying DNC couldn't use a whole lot of adjustments because honestly, all three of these jobs need them still.