SchizophreNick Late answer sorry, am reading through the chain and will answer accordingly. So OP have really good suggestions, but their suggestions are true to this build we're commenting on and using Spine. The version you talk about is essentially a whole other build in it's essence, even if it's very similar.
I am playing a very similar build using spine, like I said earlier, with my actual inspiration for the build I'm playing coming from The Curse and his video on self-ignite and using the ward mechanic that got really nerfed/fixed. My version is also incredibly scuffed since I'm undecided what to do about it. Definitely check out his video on this for more inspiration! It's an entirely different build though using necrotic damage mainly and another main weapon.
Another quick point, there is a belt that causes you to self ignite called Immolator's Oblation and I'm currently lacking that, I need to test my build with that belt before saying anything about it. I do think that belt will cause your damage to sky rocket, including single target.
However, I do think OP is onto something with his suggestion, if you wanna stay something similar to this build and still use Infernal Shades, that's the best suggestion for damage. I think that if you wanna use the explosion part of the skill you need to build it completely different. I can't answer that part unfortunately.
Chaos Bolts have been my MVP though, follow the build planner OP posted. I want to warn about The Burn being bugged with Chtonich Fissure though, but I don't know if it's bugged if you only use Infernal Shade (but if you use the explosion part you don't wanna extend the duration anyway). The bug is that it causes the game to go down to 0.5 FPS essentially, use at own risk.
Good luck!