The Spell Focus Mastery 5 was a typo (now fixed) and not relevant since I had +6 slotted in augments.
Whether you slot Quality Spellpower 24 or get it from the Dread Curse set as Profane USP 25 doesn't matter. It's the same net.
Force doesn't benefit from MRR reduction.
Let's see your gear set. Don't bother if it requires a double gem set bonus.
What sources are those? I purposely don't include Reaper stat hat, or Reaper ring enchants in the calculations.
Everyone not a Feydark Sorc struggles with DCs in Legendary Droaam.
you can read "DeathTitan Cold Druid" for all sources of DC: I think that charisma based classes can get more DC from filigrees/race than wisdom based classes.
I could agree about the "MRR" reduction, but your main dps sources would be ruin, greater ruin, dragon breath that use only fire and force (I didn't compare eldritch blast dps with ruin/greater ruin/dragon breath dps), you are not using holy fireball in exalted angel tier 5 that uses light+fire spell power, you are using healing pillar so you are not using sun pillar with light spell power: trust me that the mrr reduction impact of your eldritch blasts using evil instead of force spell power is not noticeable.
You could use "Reborn in Fire" in primal avatar destiny for self healing and aoe dps (I didn't test reborn in fire dps with an end game acolyte of skin fire focused dps build).
If I were in you I would focus on evocation and necromancy, getting +3 necro from Draconic incarnation and +3 evocation from Fatesinger, mass hold should work anyway, forget about light spell power and flamecleansed fury set (find another set and try to fit somehow the +15% artifact bonus to helpless damage, maybe taking a look at the 2 new droaam sets obtained with only 3 items), take epic spell focus evocation and Spell Speciality Necromancy at level 31 for +3 more Necromancy DC, embolden feat for +2.
You should aim for 130 Necromancy DC in my opinion because I noticed that mobs were saving my burst of glacial wrath (fortitude save) with 125 DC in R10 Droaam quests and if I'm not wrong instant kill necromancy spells suffer of a further -6 penalty in reaper content.
My idea of warlock is Crowd control + instant kill focused, with good dps (but not maxed dps) and probably would not include ruin/greater ruin (depends if I can reach 130 necromacy DC with ruin and greater ruin among my feats).