Your Dark Knight players are unhappy. あなたの暗闇騎士プレイヤーは不幸です

[ItsUrBoi]

I think the overall ideas here are great however a few things worth mentioning:
1. An invulnerability shouldn't be anything else other than an invulnerability. Regaining health fast to full and then going to 0 after 10 seconds is ok, but the other resources no. People can use it offensively. Instead I have another idea. ( 2 )
2. Instead of Living Shadow at level 90 , add a trait which makes Fray fuse with you, and grant you a massive regen on ( blood and MP while granting access to 10 Darkarts empowered actions or perhaps a new combo )
3. C&S frequency should be 30 seconds, instead of 18. To align with raid buffs.
4. The combos you mentioned could be tweaked a bit to look like one ability flows into the other. ( using Powerslash -> Souleater doesn't seem to flow well, does it? )
5. Darkarts could be an off GCD with a CD of 5 seconds to augment 1 action ( GCD / OGCD ) changing not only its potencies but also the animation.

One suggestion of mine without scrapping the kit would be to make DRK Living Shadow grant SkS and a new combo ( that combo granting you access to Darkarts as well ). Kind of inspiring from Reaper's idea of you gathering resources and using them on a big spender which makes YOU go crazy - not a shadow that you can forget about.