Fixing AD is as simple as splitting it from C&S. Making it cost 3k mana and extend the darkside timer. And allow it for when TBN breaks you get a free edge, flood or AD.

Fixing Dark Mind is as simple as giving it 10% physical damage mitigation as well.
Fixing Dark Missionary and Heart of light is as simple as giving them the faint and addle treatment where they have 5% damage mitigation for physical attacks.
Fixing TBN is as easy as providing a regen for half the damage prevented or essentionally 12.5% of your max health over 10s and making a weaker version for lower levels.

Small tweaks to DRK can go such a long way. We dont need drastic changes. Just quality of life changes.