I love to see anything that helps differentiate OPR from 40k, and I think the way you used Havoc Brothers in this story is a perfect example. I really enjoyed the small drips of Arrago and Beras's past as well, and the thing that would have really elevated this story for me is expanding on that. I think you could have spent fewer words on establishing the battle and its stakes, and used that space to really let their tense relationship shine.