DRK Tips?

[Undeadfire]

The main ability I’m not sure I’m using correctly is Dark Mind. I assume it’s meant for tank busters? Also assuming most tank busters are magical? In boss fights pre-70 I usually pair Reprisal with Shadow Wall or Rampart for busters. Post-70 I use TBN and maybe Reprisal.

Reprisal on raid wides. There really isn't any busters when you out gear content, only Savage/Ultimate continue the aesthetic till a new Savage tier is out except Ultimate. Use for free value, or save them for the mass pulls.

Mind you I’m not a tank main, and I typically ask the healer after the first boss in each dungeon if I’m doing okay or going too slow/fast. I’ve been that healer and I always wanna double check.

If you're doing Wall pulls, then you're doing fine, no reason to ask Healers what they think. There's no "playstyle" in 14, bunch of nonsense, it's perform what is required.

Any tips for Dark Mind? Or really anything else DRK specific?

This is something you need to learn on every Mob/Boss. ACT/FFLOGs can tell you every targets formulas, really isn't much to tell you other than that, use for value.