For Reavers people do use them, but how to use them and their gear will depend what traits you are going, give Cursed blade or Red Grief then put nothing on them, keep them cheap. If going Test of Skill Blasters/Heatlances are fine. You can always put Grav talons on tho for MW's on the charge.
Blaster or Shredder on kabals, no heavy weapon, they are not worth it.
You can run all Kabals and Wyches with venom back up, but if you do you will lack damage to tanks/MC i would go Test of Skill at that point, and add Blasters to kabals. Taking a Flyer, Ravagers, and maybe Raiders does help with big things, but you can make a list without them, its just going to be harder to play as you will be filling that role with mix units, the wrong mistake means its harder to kill your targets.
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AoS: BoC 9k, CoS 3k