Either way, points in Dark Arts are wasted if you are using the succubus + Lash of Pain glyph, and nothing (that I know of) suggests the Felhunter will be doing more damage than this combination.
If you would like something to be thankful for, this means we will essentially will not/will not greatly benefit from using Soulburn + Soul Fire, meaning there should be serious conversation over whether using Soulburn + instant Felhunter + Demon Soul is now more appealing. In this case, Dark Arts may be worth it, but simulation data would be nice to see.
Regardless, this is the spec I plan on running:
Reading through the posts, you are the only one underlining Affliction DL is on top, but this guide is structured to maximise Affliction Shadow Bolt spec.
Going for Drain Life as filler makes Bane useless and Dark Arts indeed more valuable (Drain Life is another DoT, Felhunter will outdamage Succubus like when Drain Soul is applied). It isn't mentioned, though, if there is a breakpoint below which Affliction SB is better than Affliction DL. Has anyone tried to define a limit between the two?