Article from Sports Illustrated:
Why Longhorns Commit Arch Manning's No. 10 SI99 Ranking Is So Polarizing
The truth is that no one has seen enough of Manning on the field or in camps against high-level competition to justify his other-worldly expectations.
Whereas Dante Moore, Nico Iamaleava, Jaden Rashada and Malachi Nelson have all gone head first into the fire in one way or another.
After a historical state title run his junior season, Moore dominated the camp scene this offseason. Iamaleava has arguably the best physical tools of any quarterback in the last decade and out-threw just about everyone this summer in camp settings.
Rashada and Nelson meanwhile play at the highest levels of California high school football and have done nothing but dominate on those levels of competition and be wildly impressive in camps and national 7-on-7 tournaments.
Outside of Isidore Newman's low-level competition, Manning did not participate in any offseason camps or national competitions, making it nearly impossible to truly compare him against the best of the best.
That is not to say that Manning is still an elite quarterback talent. He likely has the highest floor of any quarterback in the class and was seriously considered for the No. 1 spot even without the offseason work in the camp scene.