I don’t think you do want your child to study all religions equally OP. There are hundreds of them. Just as I don’t think you want your child to study all history equally. All subject curriculums have to select what they study out of a vast range of choice.
You are applying standards to religious studies you don’t apply to other studies. And that shows your attitude is based in prejudice.
Even if you do want your child to study all religions, that isn’t an offer at the school. Feel free to teach him this in your own time, if you believe it to be important.
But overall, the prejudiced attitutude that religion uniquely is one where you have to believe it to study it, is so stupid. It bugs me. Religion contains so much of humanity, history, architecture, art, sociology, morality and ethics,literature, archaeology, poetry, war, culture, ideas, I love it! It’s fascinating. And it’s so relevant to the modern day and modern threats we face. So many people comment confidently but wrongly on modern issues as they simply don’t understand religion and a religious worldview.