In this country, and amongst the demographics that attend Reading, 21 Savage is bigger, or at least the same size as Roan. In the UK, she hasn't had a single song get more than 100,000 combined streams/views/purchases. Neither her album.
Sure she might have a new album coming, but right now she has 2 songs that have made it into the UK. I can't imagine a single headliner having just 2 songs that your average vanilla crowd will sing along to, Halseys a flop in the UK and she had more substance when she headlined.
But then again, FR are the masters of giving us headliners that have achieved sweet-FA at the time, but kids look at the poster in 20 years and think "omg that lineup was insane as if they had all those" (I.e. 2018).
Has Hozier been big since Take me to Church? I know he was the soundtrack to Dark back in 2020, but didn't know he was still a thing.
Central Cee bigger than Jorja Smith you think? Sure he gets a crowd but his lice sets have been awful in recent years.