Find it quite odd how the buildings, walls etc can give you +attack etc when you are sending your troops out to the dungeon how is a wall that is back from where you set off going to help the troops?!-lol.
Also noticed on the combat in the rule book the buildings don't act for your defence unless you need to discard a building?? like when "Sean" in the rulebook had to get rid of his temple because all his army had been defeated.
Logically, yeah, the walls giving attack might seem strange.
On the building defense questions, while I understand your point, it *is* consistent with the damage rules in general, where anything damaged dies (and the defense value isn't so much resistance to damage as it is absorption of damage in a dying effort).