I imagine the Raptors have the mindset that they are akin to the most viscious of predatory birds. So they messed with their helm-vox to allow them to scream and hunt in packs, picking off those at the edges or who have been seperated or look vulnerable. But, keeping the bird theme in mind, it wouldn't surprise me if those thoughts, if strong and integral to how the Raptors view themselves, are worked on by the warp, maybe changing their bodies first, causing them to have to seek-out DarkMech help to change their armour. Or maybe the change was simultaneously organic and armoured, with their feet changiing as their boots did, the Raptors needing no help at all. Or any set of circumstances in between.
Personally, I think the Raptors' conception of what they embodied was what the warp worked on, their bodies and armour changing together. I see them as being really birdlike- aggressive, but a bit dim- happy to work for those who will promise them sport, weapons, support and more sport! I would imagine Raptor Lords are rather rare, although those that have the aptitude to win such power are incredibly dangerous with a mind that could think its way through a corkscrew, without touching the sides.
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