I recall watching a youtube video where they compared about 7 Zep songs to earlier, original tunes from other artists and they were all a spot on match. Zep stole a bunch of material.
Lots of musicians “borrowed” bits from others dating at least back to Beethoven and Mozart. The only clear cut case of absolute theft that I agree Zeppelin stole was Dazed and Confused. There was simply no justification for that.
Most of the songs on their first four albums were basically cover songs, mostly unattributed.