I strongly disagree. There is nothing to suspect that someone like Coldplay won't do stadiums in 30 years. They are kind of doing their best to lose their status with releasing one mediocre album after another, but they are not declining at all.
For some of the others we will have to see, but I don't see why someone like Adele, Lady Gaga or Beyonce should suddenly become less popular. I'd even argue in opposite to lots of the rock-band-stadium acts like Foo Fighters or RHCP, they have the chance to keep staying relevant in the general musical zeitgeist, cause they proved themselves to not only be top performers, but also their artistic output is still top-level and feels fresh.
If you look at the list of highest grossing stadium tours of all time, even adjusting inflation, 5 of the Top 10 are by newer artists.
It's Olivia Rodrigo, Sam Fender and Rihanna, but it's actually a fake-out, and each night the Bad Seeds storm the stage to play one of the late-era trilogy in full.
Push the Sky Away on the Friday, Skeleton Tree on the Saturday and Ghosteen on the Sunday, followed by an extended encore of From Her to Eternity where security all don Warren Ellis disguises and perform synchro dances.