I find the distinction between compatibilism and determinism to be incomprehensible.
Suppose that determinism is true and incompatible with moral responsibility.
Then, person A might hold person B morally responsible but according to determinism, person A was hardwired to do this, so we can not hold A morally responsible for holding person B morally responsible (and even if we were to hold A morally responsible, our holding A morally responsible can not bear moral responsibility). In other words, A can hold B morally responsible.
So, then, is there really a distinction between compatibilism and determinism?
If, as you suppose, determinism is true and incompatible with moral responsibility, then--you're right--no one is morally responsible for anything. What follows is that compatibilism is false. If compatibilism is true, then determinism is not incompatible with moral responsibility. Determinism and compatibilism are not the same thing. Compatibilism might be true (i.e., determinism may be compatible with moral responsibility), and determinism may still be false. Compatibilism concerns only the compatibility of determinism and moral responsibility, not the truth of determinism.