I think its simple in sense that the way DRK play is keeping your manna pool low and you use DA after syphon put you above 2400 to use it on souleater. in that sense TBN is no relyable because most of time its grayed out due u have no manna.

In order to use TBN u need start doing instead 2x rotation of soul chain u use TBN in end and use Bloodspiller after.
Allways keeping manna between 50%-80% and using DA only when u hit 95% manna to avoid cap.

That req extra that u dont need do whit PLD shildron nor war raw.