Answer
It depends on underlying assumptions:
- Assume that consciousness is intrinsic
Then a materialist view would consider, as OP indicates, that either they are both conscious or both aren't.
- Assume consciousness is an addition to the physics of the system
Then this remarks the extra option that one could be a zombie even though the physics are the same.
So the Zombie concept is actually a way to detect the pre-conceptions of the philosopher using it.
Thought Experiment
For fun, we could also ponder a redefinition of Zombie that leads to some interesting questions.
Imagine a Zombie that is almost like us but it lacks functionality that would – hypothetically – give rise to experience.
If Zombies operate without the brain structures (and connectivity) needed for consciousness to happen, then:
- Why do we have subjective experiences? (we could still operate in the world without these.)
In this way, the Zombie hypothesis seem to be illustrating a question. The question, as said before, now in other terms, is:
- Why do we have structures that give rise to consciousness when we don't need them?
- But then, Don't they have a function ?
- Are they just a cool side-effect of evolved and selected structure ?