I think your analogy is flawed. You assume that any attacker that breaches a layer of defense will do so by breaking the encryption or by stealing the key, but that doesn't have to be the case.

In your analogy of the bank robbers, the robbers might exploit a weakness in an exterior wall, and gain entrance to the lobby. The other locked doors will still prevent them from robbing the vault.

Let’s say an attacker compromises a machine that was joined to the mesh network via a pre shared key file (not a hardware key). The attacker still doesn’t posses a hardware key, so the higher level checks are still valuable.

Another way to put it is, that attacker is walking a part of the vault floor, but still doesn’t have keys to the lockboxes.

What you’re describing is simply multi-factor authentication.

What I’m focused on is the repeated authentication on multiple layers of the network stack. It just isn’t necessary. Either your authentication mechanisms work at the lowest level, or they’re broken across the entire stack.