Am I missing something about DRK?

[Allyrion]

Dark passenger is twice as efficient mana wise as dark arts...

I will look into toggling darkside, but its mana cost means you'll have to be at least a couple mana ticks in to make up for it, not to mention lowered damage, obviously.

If you're comparing to DA-SE. It's more efficient on Carve and Split for damage and mana is more useful on the CDs.
I guess you can save mana by doing a Dark Passenger instead of a DA-SE in some cases, if you don't care about the heal.

But you just can't sustain using it in combination with the usual DA.
My mana for just potency is already going to Carve and Split, I feel like the rest should be doing something for survival.

I'd only advocate Darkside toggling during things like phase changes.
Ideally, you shouldn't have to take it off where you'd actually lose much damage.
And yea, it does take a few mana ticks to get mana positive but it doesn't take that much when you've got the reduced in-combat regen.