I imagine a wraith plasma mortar would be pretty much useless against any immortal above red for the simple fact that dodging would be trivial, a scorpion tank shot is probably a slow but still relevant powerful projectile at green levels, because greens are that bullshit fast.
Also wonder if Zhengui could figure out some fragmentation mechanism next for this ability. Encase the burning orb in a shell of wood then detonate when it get's near a target flak style with the splinters shredding them up. Depends on if the shot is literally just fast moving lava which doesn't tend to explode or an actual explosive projectile I suppose, though that's not too big a change to make.