I'm bumping this to see if anyone else has any further thoughts on this combo. I tried one over the weekend and loved it! The character got to 31 in practically a single sitting and felt pretty impactful while running through Posi 1 and 2 and Penny Yin.
I do have a question. My thoughts are to grab what I want from Fire/ and /Dark (basically everything except the T7 and T8 /Dark), then pick up Leadership and my epic pool (Dark, Soul, or Mu). Most/all of my other characters also take the Fighting toggles, to the point that they feel like a power tax the way that Fitness did once upon a time. I'm thinking the debuffs on /Dark are strong enough that, when combined with Hover, Maneuvers, and eventually set bonuses, I should be okay without Fighting.