/sch is the best sub for single target mp-healing for a non-mage sub. You have a slightly smaller MP pool, but you have Light Arts and Penury, which effectively add 20~50% mp to your pool when coupled with sublimation (which stacks with all refresh gear except rdm's Refresh).
On top of healing you get the spells dispel and sleep, which will either let you save the QD charges or help you if you're waiting on the timers. Both spells stick reliably well for a sub. Aspir and drain can actually do quite a bit as well.
However, /sch does have some draw backs. It doesn't have curagas, it doesn't have any enfeebles (dia II is prolly the only important one), and the big one if you're going to be /mage, No Stoneskin or Blink. The main differences are if you need erase or if you fear being hit with high damage AoEs. SS and blink can be very important on what you're fighting, although I'm not sure how squishy corsairs are.
At the same time, /dnc isn't something to ignore. Drain Samba II can make a big difference even without using tp on waltzes. If you have a joy or m.kris, you'll be able to get quite a bit of tp so you can toss out curing waltz II or divine walztes. Dancer sub is great because you don't need to worry about mp, and most people don't have access to /mage with 500+ mp. I'm a big fan of dancer since it has some unique debuffs as well as pretty solid healing abilities all while allowing you to melee, even if it is weakened damage, it's superior to having to worry about mp. If you're doing nyzul, the added damage could be vital for trying to clear certain floors given limited time.
I'm a big fan of /dnc and use it any time I need to do some healing, but can still melee. On more dangerous things I tend to go /sch and stay at a range.
80 Pup Brd, 75 War Rdm Drg Sam Mnk Pld Bst Thf Whm Nin Smn Blm Rng, 72 Drk, 63 Cor, 50 Blu, 40 Dnc Sch