It's been rumored for a long time that Jimmy Page stole melodies from other songs. Don't believe it. Listen to the song 'Taurus' from Spirit (available on Qobuz & TIDAL) that was published well in advance of 'Stairway to Heaven'. I never liked Page's style of playing lots of notes at the mercy of carrying a memorable melody. Page couldn't hold a candle to guitarists such as Hendrix, the late Jeff Beck or Eric Clapton.
As to Plant being the greatest Rock & Roll singer, I've seen him in Led Zepp several time in S, Florida in the late 60's and 70's in small and large venues and he's nowhere close to Freddie Mercury, Roger Daltry, Rod Stewart or Paul Rodgers.