I think the case for Rivera, is he took over a team with the #2 pick the year before, and won he division. He did that while battling Cancer, and using 4 QBs, including 1 who was so bad they cut him. On top of all that, is a FO being sued, the owner making an ### of himself, and the team's name being changed.
True, the record isn't the best, but I think some other factors, including off field stuff could, and should, come into play here.
My case against Henry is just I don't think his season was as impressive as kelce's was. Maybe if Henry ran for 2,200 yards in 15 games it would be closer, but kelce broke the single season record without even playing week 17. He may have lead the NFL in receiving if he hadn't, which is unheard of for a TE.
Kelce was unanimously the best player at his position, other than maybe Aaron Donald, I don't think that consensus exists anywhere else.