No comparison.
Diana's funeral had 32.1 million television viewers in the UK, only the 1966 World Cup final was higher (and factor in the millions that lined the streets in London to see her coffin go past who weren't able to watch TV that day, so really it's the most viewed event ever in the UK).
It was also a global event (as evidenced by the fact the song (re)written for her by Bernie Taupin and performed by Elton John at the funeral went to number 1 around the world (from Japan to Australia to the US (11 million sales there) to Europe, with it selling 5 million copies in the UK, more than previous record holder Do they know its Christmas by Band Aid). Attendees at the funeral, from Tom Cruise to Nelson Mandela to Pavarotti. Her catchment covered so many bases, from regular celebrities to political leaders to religious leaders. Also recall George Clooney having a press conference following her death.
The most photographed woman on the planet, being chased by the paparazzi to the very end (with her, the golden goose for the paps, generating huge sums in obtaining an exclusive image of her), she also died in her prime in tragic, sudden circumstances, which elevates the shock and thus draws viewers.
All that and the era she died, when the media was largely tv and newspapers, so more streamlined, audience less spread out, so more focused, and Diana dominated the headlines.
Mania is the appropriate term to describe the whole week of her death. Never has there been a public reaction like it (a legitimate reaction, not the fake, under duress North Korean public reaction when their dear leader dies).
The scale of Diana's funeral can't ever be surpassed because of the combination of the status she had, the shocking circumstances of how she died, and the era she died when media was global but also concentrated with fewer outlets.