(Had to fire up the game to refresh my memory on the exact wording)
“Boon – Your men gain 40% more experience.”
“Burden – Your men gain no experience for allied kills.”
I agree with what you are saying about xp gain from kills by non-player controlled characters.
I guess I did neglect to mention that there were no allied peasants/caravan/house troops/etc in the two battles. So I’ll say that now – there weren’t. I didn’t even deploy any wardogs/warhounds because I didn’t know whether or not they counted as allies.
I also failed to mention that the 2 Oathtakers (Kettilmund and Arne) have the Student Perk for +20%xp. The other two do not. Further, none of the bros was under the effect of a Training Hall xp boost.
I think the zero xp gained by (zero killing blows) Jahaf in the second fight is the critical clue. I’m now fairly certain that “allied kills” includes all kills made by ANYONE other than the bro in question. This would be strange to my way of looking at things, but could be implemented legit-ly if that’s what the developers were aiming for. But if all xp for a particular kill is being divided up among the bros of your company as normal, and then everyone except the killing-blow-bro has his share reduced to zero … that is NOT okay! A 40% xp boost doesn’t begin to make that a net “boon”.