I can't remember where the post is but from what I can't it was Olivia, Fred, Rihanna. If that was the case, I can see see two of Catfish, Yungblud and Biffy Clyro making up the subs. Stick Charli XCX, C&S and Nick Cave on Other with Charli/Cave being an option to switch with Biffy. You can't just say it's 3 guitar subs either with those 3, Yungblud is way different.
The only headliner I'd question there is Korn and even at that, it seems an easy one to get away with for me. I'd say the same about a potential NIN headline spot too.
As part of a good complete lineup, they'll be fine.