First, Surely each defended settlement should have a hidden tunnel , opening far way from the settlement, that friendly soldiers can use to slowly gain access to and from. There is no need for these "Break into" casualties.
Similarly, second point, Attacker in a siege SHOULD take casualties in the Siege initial setup phase - clearing paths for towers / rams etc, filling moats etc etc. these were very dangerous tasks. Yet, in BL ,no casualties.
Why is this game so biased towards attackers ?
Yes and no.
I agree there should be such things from a historical pov yes.
However those types of entrances etc was atleast in the sources I've seen been relative small - read 1 man standing, not 2 men shoulder to shoulder wide.
Then you have the logistic of it.
You really think that theese siegers wouldnt notice an army of 100-250 units sneaking by in the area, and all just vanishing into the rock wall.
The ones I've seen of such things, is more used for escape of the besieged and not to reinforce it.
Bascially what I'm saying is that the current system is more "realistic" imo than anything else.
You could maybe send in a squad of forces, but a full 1 man army or a armygroup - I doubt that.
When you historically have had sieges they surround the settlments all around it unless its shielded of by some natural hurdle/obstacle (like steep mountains or water etc)
I personally like that there is casualties to entering such sieges, to have you actually "risk" something to a degree, so you end up with lots of your t5 troops dead, which will make the siege-encounter harder aswell.
As for the other point on the besieges takeing casualties while setting up - yah I can totally agree with that one.
Archers on the walls takeing out attackers as they are building equipment and placeing defenses etc.