The main key to this build is taking advantage of ROPO. Every time you cause damage, you heal, so you want to always be causing damage.
Swallow Soul is a bit of a flex spot. It's primarily there as another damage skill with a bonus heal over time. If you need more healing while still keeping some damage, you can use the other morph - Funnel Health - or if you just want a burst heal as back up, you could exchange it for Resolving Vigor. If you feel you're getting enough healing from ROPO and want more damage, you could exchange it for one of the Cripple morphs (Crippling Grasp/Debilitate) or an Assassin's Blade morph. Shadow Image/Dark Shade also works well.