That's one view point. In the days before books, radio, television and the internet, people spent a lot more time sitting around the campfire talking.....about 200,000 years worth of talking.
Like you and I, they pondered the meaning of existence. Depending upon the region of the world they lived, a consensus developed. All tribes/cultures have "origin" stories. For some reason, at least in the US, only the Christian origin story is ridiculed. Atheists don't ridicule other religions and cultures for some reason, which I find curious.
That said, as human tech advanced, those stories were eventually written down. For Jews, Christians, Muslims and Mormons, Moses (either a person or a small group of people) wrote down the first five books of what evolved into the Bible. Regardless of the writings used, the written beliefs became the cultural norm for human societies for over a thousand years before radio.
Before the printing press was invented in the 15th century, a tribe or village might only have one book. If they did, in Western Society that book was a Bible, usually held the the local priest. Very few villagers had the time to become literate because they were too busy trying to stay alive. After Guttenberg, lots of books were printed, but the best seller remained the Bible.
Less than a hundred years after the mass printing of the Bible, Martin Luther published his Ninety-five Theses and a slow explosion of various ideas followed, including literacy of the population. Yes, the rich learned to read first and the poor last, but literacy spread.
Back to your point: I disagree. Yes, powerful assholes seek to dominate other people. They'll use whatever tools are available including, as Marx wrote, the opium of the people. No tool is evil, wrong, bad or even good, right. It's just a tool. It's how it's used that matters. Yes, evil people have misused religion just like evil people have misused other tools and forms of power. Your claim that religion is only like Marx claimed is wrong since it's much more than a tool of evil as evidenced by the good people have done with it.