"They might be (not my own favourites, but I can see why people would like them), but does it make them a headliner of a (world-class) festival? Not saying I wouldn't want to have them on the line up.."
Just for reference, Phoenix headlined Lolla in 2009. That was the first year they had proper headliners on both ends every night of the festival. It was sort of regarded among the Lolla Board as a "promotion" to US fest headliner status for Phoenix. They also got high bookings that whole tour, their album sold well, and they got really glowing endorsements from all corners of US pop culture.
Didn't wanna re-tread this on the board like I was lecturing you, just wanted to fill in the blanks.