I agree that these are not exploits. Every game that has a base building mechanic also employs base defenses. The only base defenses that this game allows are 1) physical barriers or 2) you running around with a pack of wolves trying to personality kill all the attackers.

There should always be these 2 options. A passive one (barriers) and an aggressive one (fighting).

If barriers were "nerfed" somehow, then new defense capabilities would have to be provided, i.e., catapults, boiling oil pots, crossbow turrets, etc., but these things lend themselves more to multiplayer and not to solo. They must be manned and aimed; automation is a little sparse in the viking world.