I didn't mean to imply that lords were fighting bandit parties that were stronger than them. I'm saying they spend part of their time patrolling around settlements clearing out bandit parties. They can take losses during this process just like the player. Here's a quick example:
And
here's my source that they clear out hideouts. I'm simply saying that a lord's sole motive is
not to just seek and destroy the player, so even if they spawn with 10% of troops they are programmed to have other duties that they will carry out, and need troops to do so.
Also, lords that are defeated in battle (and don't rout) will
always be captured; they do not instantly respawn. The average time to escape for an AI lord taken prisoner by another AI lord ranges from roughly 2 to 4.5 days. This essentially acts as a "cooldown" like you were talking about and isn't drastically different from the 3-7 days that you suggested. They
do have a chance to escape before then which can make it seem instantaneous, but that's the average time to escape.