I can't recommend something I haven't read myself, but Mircea Eliade's "History of religion" looks good, but it's quite bulky. I was considering it myself, for the same reasons as yours. Maybe someone who read it can elaborate. I'm reading his other work about yoga, and it is quite interesting. I you look for basic basic understanding, maybe "The religions book" could be of help. I'm occasionally reading "The philosophy book" from this series, and while it very brief, I find the format (brisk to the point summaries, graphics) quite good for what it's trying to achieve.
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