Christianity isn’t claiming to have invented morality, just the morality you pretend you would have had without it. Many systems have moral standards as you correctly pointed out. But moral standards you believe are best are based on Christianity.

The book isn’t making claims about what right and wrong is, it is simply tracing the things you think are right and self evident back to their origin which was specifically Christianity, and not any other moral system. Read the book, it’s not some moral treatise. It’s a history lesson as to why you think right and wrong are what they are.

Though your statements about Judaism and Christianity are mostly correct, that still doesn’t make Christianity as Bronze Age thinking religion. You are smart enough to know that. It’s also plausible that Moses became a prophet after the Bronze Age ended. But of course you knew that already since you are an expert in ancient religions.