Excellently put, in essence Druchii "culture" as it were is non-existent. A weird argument to bring to the table but one that has it's reflections. They are essentially an army, divided into camp and battle. The time scale that the Druchii and Asur work on let this be a thing. EX: the Long March that the Asur will go on is in essence the reflection of Druchii raiding. Low(ish) risk for high reward for each of them.
Asur do it to make sure the waystones are up, doing the battle of their long war away from the frontlines but battling what could be viewed as "insurgent" forces.
The Druchii is gaining experience, being blooded on patrols through claimed but not controlled territory, whetting them for the true battles to come.
The grand majority of Druchii (if not all) view Ulthuan as their homeland still, inhabited by traitors who pushed them out to their former frontiers. The palaces they have are nice, but it isn't
home. The Druchii are essentially a permanently campaigning army and it seems Malekith likes them that way. When lifetimes can measure millennia it brings a different attitude for war making, especially with your leaders never changing. To the Druchii and to a certain extent the Asur, everything outside of them is lesser, not in a small way either, the war that has defined their species for millennia at that point?
All the talk of "culture" on behalf of the Druchii it could be argued arose out of military necessity. Soldiers getting bored in camp away from the front lines? Well Khaine is there to keep you sharp, those slaves will be tasty for him. War taking longer than expected? Raiders now plague the sea-lanes, again keeping sharp but directing wealth to pay for the soldiers. Soldiers need to eat? Enslave some humans, what do we care about them, they breed like rabbits! Every outlook leads back to Malekith, the ultimate ruler of Druchii society and his Mother, the heart of it, they don't care about Naggaroth, they care about their rightful place on Ulthuan. Anything that exists in their purview must be put to that end.