I think that Gallowglass picture, and the large body of contemporary writings of them, probably tells us quite a lot about how they fitted into any army or raiding party. The fact that they had two "serfs" to carry their weapons & armour seems to have contributed to the remarkable speed the Gael (& i'm assuming Viking also) armies could manage over rough terrain and still be capable of battle afterwards. Just like alternating walking and running while marching, I bet they shared the job of carrying the arms, thereby extending the duration of stamina for everyone involved.
These serfs weren't slaves, they were just low class but obviously would still be in this proposed military caste, perhaps young, probably under training of their masters. In the Irish caste system a lower class person could rise (or for that matter change caste) by a wide number of methods, including by merit of deeds done. So military serfs trained in weapons, and must've helped out their immediate "masters" during the battles, but whenever we read of Gallowglass in battle - they are shock troops & choke point defenders - we never hear much about what their serfs did. Although I did read once that a serf was raised to Gallowglass status after picking up his fallen masters weapons in combat. It makes sense that they played some support role, perhaps finishing off the vanquished as they advance, or as Slingers - an ancient (plus mobile, effective & cheap) warrior skill all military caste children would learn long before they can train with swords, and yet we stop hearing about them as a battle formation around 1000ad.
Btw thats why I mentioned Gallowglass in the first place, because no modern scholar would argue that they - with their serfs analogous to a knights squire - weren't of a "noble" rank, and supports your view that the primary Viking warriors were a noble infantry, not simply a rabble of marauders. But then I think we don't generally understand how things were back then, from what I've read, I believe there was a more "level playing field" when it comes to social status in the early middle ages than there was in the later middle ages, perhaps even now at least in the vast difference between haves & havenots, when you consider all wealth was based on working of the land, and the majority of people had some land... but that would be another topic.
I guess I'm kind of proposing that since we can see the direct inheritance of Viking warfare so clearly in the Gallowglass, we could assume that they always travelled in a group consisting of some heavily armoured nobles (Jarls & extended family (Huscarls?) perhaps?) with then ~twice as many support as light troops (~Carls, Thralls etc?).
