Ok, every legend slot artist (with the exception of Kylie, and they owned her one!) started their career in the 60s or 70s. I know that's a dwindling crowd but still a good starting point. If they can sell out stadiums (think Madge, Billy Joel) they are headliners. Legends are generally Arena filling artists. Of note, ELO are the only band to play. But take Ray Davis [Kinks], Brian Wilson [Beach Boys] in to account.
There was a rumour of Roxy Music for 2023 Legends slot that never came to fruit. I'd say that were more WH Headliners, like Bryan Ferry did in ?2014.
Eagles announcing a tour makes them in play but I think their fee would be huge.
Barry Manilow was on tour recently and he fits the spec 110%.