You say you dislike coalescing shadows because “Dots are easy to remove” but then Insidious ire requires all 3 dots to be on the same target to do anything.
Pain of death is just really, really weak, and the proc from deathspeaker doesn’t scale with the number of targets you have dotted with pain and is also pretty weak.
Coalescing shadows alongside puppet master give you very consistent stacks of coalescing shadows that spend to basically give every spike and blast you cast a solid 10-20% damage boost. Because of the frequency of everything the 10% periodic damage buff also has near 100% uptime.
Insidious Ire - requires one recast of VT and you can have +40% damage MB ready on target, specially with free DP and VT. I have comeback, after bypass all the Shadowlands and try to understand mechanics. Will try the mass build and will test it latter today.