Yeah, box steps stack. Don't even need DNC main for that.
I've been going to a few Dynamis' as SAM/DNC since I show up late and usually end up being the 19th person in the zone (literally... this has happened like 4 times lately). When I finally do get into a party, I can support heal and remove status effects. If I were in a party of BLUs, I would have no problem keeping aspir samba up for them.
Only thing I can't do as well as a DNC main is heal... but DNC subs in dynamis are no joke (esp soboro SAMs).
No reason not to if you can get that PT setup, very few mobs even got a chance to 2-hour. Was excellent.
In a PT of pretty much just BLU, they were keeping up their own hastes from Refueling and blu are a very self sufficient job, aspir samba 2 on every other mage mob was enough for them to get a little back at least from their swings to do some more, on top of their MP drainkiss and autorefresh from their EQ/Traits.
cant think of DNC being more useful in endgame if you already have a RDM
if DNC is your only 75 job, then it gotta be useful right?