1) Oregon loses too much talent
This is a counterpoint to the first article. Oregon is going into the next season without their biggest receiving threat in Josh Huff. They are also losing Terrance Mitchell, Avery Patterson and also may be without De'Anthony Thomas or Ifo Ekpre-Olomu. While the numbers are replaceable, what these players meant to the team is not. Josh Huff holds the record for most receiving yards in a season and was a top tier blocker in the running game. Losing both corners and a safety does not bode well for a defense who struggled against the run down the stretch. Lose 3 of 4 defensive back field starters and that D could become a sieve.
2) Growing pains on defense
Simply put, losing a defensive coordinator is going to hurt this team in the early going. It may hurt them longer than that. Players who have been in the system to this point have learned a specific verbiage and mentality on defense. Bringing in someone new is going to potentially change those things which could lead to confusion and an extended adjustment period. Not to mention that if the scheme changes, perhaps the players Oregon currently has on defense don't fit the scheme properly and that could also cause problems.
3) Mariota can't do it all
Marcus Mariota is a magician and a top flight quarterback, but he can't do everything on his own. If the Ducks are unable to get much of a run game going, then the mantle will rest with Mariota to lead his team to victory every week which is a tall order for any quarter back. Oregon is still a running team, regardless of the signal caller and Mariota is a better quarter back when the runners are running well. Josh Huff had become something of a security blanket for Mariota and his absence is going to factor large into whether or not the Ducks are going to be successful next year.
4) Both lines need a LOT of work
One of the biggest problems facing the Ducks this previous season was their line play. The guards on the offensive line were often unable to get a good push which negated any possibility of an inside run. Over the last month of the season, Oregon's defensive line was nothing short of a failure. They were dominated by Stanford, Arizona and Oregon State before they put together a gem against the Longhorns. Unless someone steps up on each side of the line, things are shaping up to be a challenge in the trenches.