They always were considered subs to the majority, I think it's only those 20 year old children that have only ever known the shoddy marketing technique of 6 logo bands that still get drawn in. But they are now the majority sales so it's a Pandoras box they can't wheel back or it looks awful.
It’s definitely changed. I can think of Billie Eilish, Olivia Rodrigo, Sabrina Carpenter, Dua etc that all blew up with 1 or 2 albums. It’s the way music works now. Stuff goes viral on TikTok, music is far more accessible through streaming. I think it will become common place for an artist to completely blow up and headline festivals with a smaller back catalogue than was probably common pre 2020.
The first time Dua Lipa headlined sziget she only had one album out.
Also who's to say that Chappell won't release anything new before her summer festival dates.
(to be fair : Roan is american, Charli is british... it helps a lot when you come from a country with 340 million inhabitants compared to only 55 ^^)
But I do feel the same : nowadays, a fashionable artist can easily be a headliner, and 5 years later forgotten by everyone..