Directly quoting from a developer:
Recruiting from raided villages. For that matter, having no apparent restrictions on recruitment in settlements, period, whereas you need to work on reputation - though I may simply be unaware of this working under the hood. Doesn't seem to, though, especially since the quote above pretty much details they get a free pass on two recruitment slots regardless of any actions taken against the settlement, or base relationship between factions. WIP, I get it, but as things are still stands.
Respawning with higher tier troops. For that matter, again - not sure how things work, but I don't think their troops' leveling up is handled the same way the player's is. Understandable given game's limitations, but still different treatment.
Income in general. Faster prison escapes, though maybe that was a bug that got patched. Then again, I'm not sure their escape chance is calculated in the same way, considering the stats of some of the lords I've seen escape. They certainly don't seem to be investing in either caravans or workshops, though (ok, this one's in favor of the player, but still different rules).
I suspect there's more, but I can't say I've been playing the game with a focus on how AI behavior differs from the mechanics assigned to the player, so maybe I'm just flat out wrong.
I really think that the player should only be able to recruit mercenaries until they have their own fief, I also wish lords could only recruit from their own fiefs. Of course, this would take a re imagining of the recruitment process. So for example, fiefs would have certain limits on how many soldiers could be recruited for each lord, etc. Lords with few fiefs would naturally have less soldiers. Infinite soldier supply is just silly. There should be ways to hurt a faction by killing a lot of their soldiers which makes them not want to go to war for a long time. Of course, someone else might take advantage of this.
While I disagree about the "only mercenaries" part (hell, the village recruits are, when all is said and done, "mercenaries" even when your're part of their faction), want to pimp out
a suggestion I made a while back related to the "notable-owner-recruitment" interaction that never got any traction.
Basically, have one notable in a settlement with a recruitment queue restricted only to the settlement owner OR their overlord(s) (lord->clan leader->faction leader). Require permission from the owner to recruit from any other notable, or, with high enough relationship with the notable, suffer small penalty in relationship with the owning lord (you went behind his back and, without permission, removed valuable hands from his property).
Bottom line, all lords have near-guaranteed locations to replenish their party, interaction with lords ends up more encouraged and useful, and more "powerful" lords can rebuild their parties much faster.