There are a couple factors in play for why Marcus Mariota has a distinct advantage over Johnny Manziel when it comes to the Heisman.
Leaving aside my theory that there will never be another two-time winner, consider these two issues:
1. Mariota is more likely to play in a 13th game.
There’s obviously a long way to go, but if the Ducks continue to win they will go on to play in the Pac-12 title game, most likely against a ranked team like UCLA or Arizona State. This gives Mariota an extra game to add to his overall production while making a final statement to Heisman voters. Meanwhile, because of Texas A&M’s loss to Alabama, it’s going to be tough for the Aggies to make the SEC title game, which means that Johnny Football will not only be sitting at home during that final weekend of college football, he’ll have one less game to add to his season resume. Note that when Manziel won last season, he did it with 12 games since A&M did not make the SEC title game last year either. But his main competition in the race — Manti Te’o and Collin Klein — also played 12 games and did not have the advantage of a conference title showdown to help their cause.
2. Mariota plays a more high-profile schedule the rest of the way
Games with UCLA and Stanford in back-to-back weeks — with the Stanford game coming on a Thursday night — plus a season-ender against an Oregon State team that could be ranked, gives Mariota at least three high-profile scenarios to make his case. Then there is the Pac-12 title game, which will be played one week before the Heisman is awarded. A&M, meanwhile, has a game with a ranked-but-not-highly-respected Auburn team coming up this Saturday and then a big matchup with LSU on Nov. 23. The problem is that the Tigers play Alabama in Tuscaloosa two weeks before they play A&M. If LSU loses to Alabama, a lot of the air will be taken out of the LSU-A&M matchup. There is also the season-ending game with currently-ranked Missouri, but with Tigers quarterback James Franklin out for the next month, that ranking may not hold up.
Of course, Mariota and Oregon could also lose some of these games, which would make these matters moot. But, assuming that both Oregon and Texas A&M win out, Mariota has a distinct structural advantage the rest of the way.