RoenTheMage thank you for the kind words! Happy to hear my neuroses and perfectionism are paying off! 😄
Effigy of Combustion can definitely be useful - it just depends on what you are doing. I would only consider it for Monos and Arena. As enemy HP scales up it becomes less useful, so you might see some annoying drops in DPS against strong enemies in monos. Ghost Maker can be used in the same way, for convenience/speed up in monos, without Effigy's chance for overwriting against single targets.
Against Mono/Dungeon bosses, I'd use the same principle for Effigy as Ghost Maker: avoid anything with a chance of overwriting your Infernal Shade.
Personally I just keep Infernal Shade > Legion spec'd. It speeds up clear times in monos/arena and is deterministic. Sticking with a wand is nice to offset mana costs, and I would use Ghost Maker for shade generation before Effigy.
But respecs are simple so I encourage you to try it and see if how it feels to you! If you have points to spare, try Awakening Presence and Grand Sacrifice, too.