Zeppelin stole a lot of their music without ever giving credit to the original composers. The only time they did was by court order. If you think that makes them the greatest band ever, then you need a paradigm shift. Without Jimmy Page, they're just another blip in the British Invasion; Plant couldn't carry the band without a great guitarist. Bonham was a good drummer, but not phenomenal. And most people don't even know who John Paul Jones is. They're good, they've influenced generations, but they are not the best group ever, by far.