mate shes ridiculously famous. I'm not a fan and it may be hard to see past your circle but her fame is undeniable. And on the note of Fred again, it's all subjective no? I personally think his music is contrived shite and there's been a plethora of interesting electronic music released at a constant rate over the past god knows how many years.
But on the note of needing the credentials or 'earning' your headline slot over a few years; it's all quite dynamic. Yes, traditionally most artists will do just that and get the headline slot when they are more established to the crowd, but some are just instantly cultural zeitgeists and can draw 80 thousand people to a festival less than a year from their popularity spiking. Just look at Arctic Monkeys, headlining Glasto a year after their debut and only a couple of months after their second. It can happen, if they can draw the crowd, they'll get booked
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.