I suspect the family and Arch himself already had decided before the year began that he would need 2 years starting in order to develop and to build his resume.
Of course, had he met all the super expectations of the media and tore up the college football field, it might be a different matter. But, clearly, that's not the case, so he will undoubtedly stay in school.
I wish the kid the best. What he'll eventually become has yet to be revealed. But any talk of drafting Manning in 2026 needs to be laid to rest and my guess is that among NFL teams, it already has been.
