I don't like the idea of levelled-up looters, but think larger groups should have some kind of leader.
I think it could be that :
When prosperity&security are low, then some peasants mutate into looters.
( there could be variation among the cultures )
The size of such groups is limited but gets a boost if they run into a deserter ( low-mid tier ) who joins them.
How big this effect is depends on the Tier of the deserter.
And for deserters itself it's similar, the number of troops of a tier is limited, but they can bind a bigger amount of lower-tier-troops.
If it get's too much cohesion will drop and a split occurs.
( so there will be no big elite-deserter groups )
And then bandits won't join looters, but they can recruit them ( this may fail sometimes if the looters have become too strong ), and if these level up they'll upgrade from T1-looters to T2-bandits.
Bandit's can't upgrade either ( otherwise there would be groups of leaders after a while ),
but there must be some stronger ones.
And at the end ( some ) minor factions have the ability to recruit bandits and then these can upgrade into faction-units, from T2 to T3, or maybe higher for the stronger ones.
So minor factions wouldn't mix up with looters, but bandits could be found mixed both with some minor faction-troops as well as with looters.
In Warband there was a big mod, in which all bandit types had one famous hero and sometimes you would see him with several smaller groups attached, much like we have field armies for lords. Was pretty fun and interesting, if you attacked the forest ranger hero when he had 200 men, "arrows would block out the sun". Something you would never see when fighting lords, since they had combined arms of infantry-archers-cavalry.
Yeah, good points. It would make sense if some of them would have a random bow that shoots sideways, a cracked spear, o a sword that is too big for them to yield properly. Couple of armors or helmets here or there.. Idea being that they stole that loot somewhere but can't even use it properly. Now their gear is more unified than some of the armies - they even wear same colour rags - should be a bit randomized. couple greens or blacks in there..
I also think that naturally every group of looters should have a leader, that is slightly better equiped than all other looters, Maybe stand behind the group "and give commands of sorts"..
I like all these ideas. Every looter looks like they're wearing bedclothes and they're all the same colour. These guys can beat groups of villagers, and sometimes even a lord that has taken a recent loss. In addition to having some armour variety on spawn, they should also be looting and using gear from their wins. I've seen AI lords selling armour/weapon junk to cities, so the mechanic of them looting gear and having inventory exists, but it just needs to be applied to looters and modified so they'll use the gear.