Sounds like the real reason you think that support DNC has a place in modern FFXI is that you play with really horrible mages.
Two good white mages (sometimes, one) can keep an entire Voidwatch alliance alive barring NMs that cast death or one-shot people with no support from even a BRD, RDM, or COR (let's face it, the WHM is just going to get DD rolls even if there is a COR in their party...which in most cases there will be).
Not being in Voidwatch implies that you're either 1.) in Abyssea, 2.) fighting enemies that are a maximum of Decent Challenge, or 3.) doing Grounds of Valor on high level enemies.
In case 1.) You cap evasion on everything in a DD set, and you can solo almost everything without shadows. Let's face it, if you're bringing DNC to Abyssea, you're either in a large group that has everything covered and you're just tagging along, you're soloing, or you're stupid. There's rarely a reason to drop saber dance, either.
In case 2.) You will very nearly cap evasion with signet and your DD set. You're probably one of the more survivable jobs just because nothing can hit you, and you have Fan Dance if shit hits the ... uh ... fan. For the most part, a Waltz V every 3 minutes (Saber Dance recast) is enough to keep you going provided that you bring remedies or remedy ointments along and are fighting enemies that don't cast magic.
In case 3.) You must be pretty bored.
You claim to understand the job well, and yet your posts point to exactly the opposite. We all want support DNC to be viable. It just isn't. Claiming your spot cures, sambas, and watered down damage are a strong enough asset to a party or alliance to merit you not being there on another job is just ... well ... either you're completely delusional, or you're playing with some really terrible groups.
It's basically the same as a RDM claiming that they are worth bringing because they can melee.