Next idea regarding attackers vs. defenses are the damage types different from charged attacks. That is, you should need different tools to take down different structures, based on their type/class.

For example, scavenger/pioneer/wood type buildings get bonus damage from Axe type weapons, while getting bonus defense from all others. This makes it so that when attacking certain walls or structures, you'll need to bring either a single or multiple types of weapons to take them down easier, even if it means sacrificing your main weapon type, and making the defense think about the type of enemies they will have to deal with.

My main damage bonus ideas come to:

Grass/Leather/Gadu are weak to Blades, but strong to Clubs.
Mason/Stone are weak to Pickaxes, but strong to Blades.
Pioneer/Scavenger/Wood are weak to Axes, but strong to Shovels.
I'm stumped on Scrapper, but since it takes such a high Architect level to build, I think maybe it can be weak to none, but strong against none either.

The idea of structures being strong to a damage type is to give the defending wall bonus defense against a certain damage type. It would make sense that a knife blade wouldn't be able to cut through stone without great difficulty. Any structure that isn't especially weak or strong against a specific type instead take the regular base damage of the attacker.