Happens a few times with me, I think it's to do with the hideout being empty when you enter it, so it automatically puts you to the leader. Usually see this when a group of 3 bandits make a hideout right after I kick them out their former one.
If there's only 1 stack of bandits that's the boss fight and you get to it immediately. Two stacks is boss + some dudes, three is boss and dudes in all spots, and third is almost always a big boost in numbers.
That's why if you move around a lot, and bookmark villages with nobles you can knock a LOT of them out in short span.
If you successively kill off roaming groups and leave them space to exit the hideout, you may find a moment when there's less groups. You can also kill some guys, exit and return to continue where you left off with full quivers and fresh troops.
There's a lot of space to improve hideouts, but if anything - to make them more challenging and dynamic as more players figure out effective ways to deal with them.
For forest bandits if you feel confident you can essentially kill all of them off yourself, then with careful positioning of your troops (and F3-F3) and engaging before effective bow range - you can make them waste time on 15hp shootout with your troops while you headshot one by one. As you said, still gotta strafe as if your life depends on it as one can always peek out from behind a hill.
Also, the game will mostly draw from units on top of your party list, although from experiences of other users this may discriminate certain units. Personally I've only got 1 recruit in the mix when almost all of my top dudes were wounded, otherwise it's a mameluke/Buccelari party.
Also: they're expensive, but if you've got mamelukes, they're amazing for lairs (heavy armour, bow, shield).