I've tried this, albeit without bind demon and with 3 tainted, but it wasnt good enough against fire immuns, and there are plenty. And this is just another fire build and we already have one.
Normal fire build is better imo. I have two warlocks in single, one was fire and one was ES. Now es is completely trash tier i wanted to try something else but its not this. I might give a shot to magic variant, otherwise just gonna keep my fire build.
But as the whole point of the build: you can be hitting an immune for up to ~17000 HP per cast of blood boil after amp damage & +/-% fire on sunder
And that
does kill immunes fast enough. That's why you need the bound demon to provide amp, whether its a venom lord or siren or even flayer shaman
The damage vs non-immunes is so overkill you can do ubers or p8 baal with it, the damage vs immunes is so weak you NEED that 2nd element to speed it up, and its right there for minimal investment: 1 point bind demon and +19 skills can get a holy freeze + cursed demon that is mostly immortal