They are written by men, yes. But the content is revealed to the author by god, no?
The differences are major. Yahweh has a son Jesus, but Allah doesn't. The Hindu god Brahman is represented by a trinity: Brahma, Vishnu and Shiva, while the Sikh god is just 1. Yahweh created the earth and the heavens as described in Genesis, but Brahman created the universe through the cosmic egg, while Waheguru doesn't go into details of how he created. The Bible talks of the apocalypse and Jesus' second coming, while the Vedas mention no such thing. Neither does Waheguru. Do these really seem like minor, cultural differences to you? Come on!