In this specific case, we have an essentially static system that's exposed to the public that you need to protect from an unknown number of attackers with subst

In this specific case, we have an essentially static system that's exposed to the public that you need to protect from an unknown number of attackers with substantially more resources than you do. To use the analogy of the plane designer, it'd be equivalent to building a consumer airliner that can handle flying through a warzone.