I agree with your point in general, and it does speak against an immaterial soul surviving death, but I don't think it necessarily apply to p-zombies. The p-zombie hypothesis is that the consciousness "property" has no causality over the physical world, but it doesn't say that there is no causality the other way around: that the state of the physical brain can't affect the consciousness. So a traumatic brain injury would (under some unexplained mysterious mechanism) reflect into that immaterial consciousness.

But sure, it's yet more epicycles.