I complained about Word Bearers a lot in the previous thread, but besides the Possessed joke they actually aren't terrible. Their tactics just focus more on their HQs than on their regular dudes.
I'm refining the method of making Word Bearers broken. This is what I've got so far:
Daemon Prince of Tzeentch with Power Armour, Spell Familiar, Psyker(Mastery Level 3), Crown of the Blasphemer
He will cost 300 points, 340 if he takes Wings, but it's alright, and here's why.
He is a powerful melee fighting monstrous creature with a 3+/4++ re-rolling 1s, who strikes with huge weapon skill and initiative at AP2. With Discipline of Tzeentch and Malefic Daemonology, he is also capable of buffing himself and unleashing witchfire, as well as... summoning.
This DP casts Summoning(which he can always take) and/or Incursion on 3 rolls of 3+. He only suffers perils on double 6s because he is a daemon, and re-rolls failed psychic checks because he has a familiar. This means he only needs 4 psychic dice to be able to summon in most cases, which he will always have(even if he's the only psyker in your army he gets 3+d6 each turn)
Essentially he consistently makes his points back in a couple turns by calling up mobs of plaguebearers, flamers, plague drones or screamers, depending on what is needed to counter the enemy list. And, he will also massacre anything short of TH/SS terminators in melee because he's a daemon prince.
But it gets even gnarlier if he rolls Sacrifice. For the small price of having to backstab one of your underlings(or take a wound on yourself), you get an exalted daemon... with the Grimoire of True Names. Which 2/3 of the time gives your Daemon Prince a re-rollable 2++.
So just take this guy and cheese it up while playing the rest of your warband as a regular space marine army.