True, +1 for a thoughtful answer.

However, I still don't see the circuit as reducible to simpler working components. Regardless of the medium across which the current flows, it still seems to me that the circuit is a simple machine - a basic device like the pulley, joint, inclined plane, or lever.

In considering this, I also think that chemical fuels are simple machines and belong on that list, as they are ostensibly devices (can be used by an agent to do work) but also aren't reducible to simpler working components.