Not to burst the whole Chappell Roan bubble but in the past 10 year only 1 Pyramid sub has played Reading & Leeds in the same year. Not to say it's not possible, just not likely. On the other hand multiple Other stage headliners have played Reading & Leeds in the same year.
Makes me think she could be up against Neil Young while Charli XCX subs The 1975.
You really cannot complain about the "size" of the three headliners. Chappell like her or not is absolutely huge. Arguably one of the biggest music stars in the world and certainly the hottest atm. Travis Scott is a stadium selling artist and BMTH have a big legacy and are huge themselves.
You can moan and pick holes all you want, but they are absolutely massive headliners.