I’d argue it’s a pretty strong prequel in the sense that it shows how Indy transforms into the scrupulous archaeologist in Raiders. At the outset, he’s a lot more like Belloch, a darker, greedier man driven by self-interest, which is especially evident in the Shanghai chapter that opens Temple. (His original motto is "fortune and glory" after all.) Hence, he only becomes the Raiders "It belongs in a museum" Indy after his ordeal with the death cult when he chooses to save the children. It’s a great character arc, though one sadly retconned/undone by the opening flashback of Last Crusade.