Well, implying that the stats don't matter whatsoever isn't wrong, but rather... Untrue. TweakMB suggests that leadership increases 'max' party size by 10 for each point, and 25 points of renown gives 1 max party size. However, this doesn't apply to prisoner stacks. A lord can carry a virtually infinite amount of prisoners around, and an infinite amount of troops, of which they take from the prisoner stack of a party they defeat. This also applies to every party on the map (I think).