Come on mate, you know that's not true. She has tonnes of bangers.
If you look at the list of the most streamed artists on Spotify, how many of these artists released their debut single/album before this century? Spotify is a Millennial/Gen Z phenomenon and doesn't always accurately reflect the popularity of older artists. Yes, the Beatles have had over 400 million streams, but it's the Beatles! Why not look for streams for other older Glasto headliners down the years, such as Springsteen, GNR, Rolling Stones, The Cure, The Who, Metallica, Neil Young, Stevie Wonder, et al and draw a comparison there?
Also you're right, she laid the foundations for pop music. She is arguably the most influential artist in the genre. No Madonna, no Taylor Swift, Beyonce, Dua Lipa, Lady Gaga, Britney Spears, Rihanna, I could go on. That's like saying The Stone Roses shouldn't headline because Britpop artists took what they did and made it bigger and more successful.