Now on the face of it, one would think that the answer to this question is a resounding "NO", as Robert Griffin is a far more important player at a tougher position. While those points are absolutely valid concerns, that isn't the whole story though. In fact there are a number of reasons why LeRibeus's absence have a greater effect on both him and by extension the Redskins over the long term. (Update: when I first posted this earlier it wasn't clear I was talking from a long term perspective)
Now there is no argument that quarterback is a tougher position to learn in the abstract, you have to remember that Robert Griffin has a lot of advantages, despite the fact that he is learning a brand new playbook and style of football. Redskins coaches have been working with Griffin since before the NFL Draft, not to mention that he stayed late during OTA's and Minicamp to further learn the offensive system. LeRibeus hasn't had that level of coach interaction, film work, or time with the team. Which makes time at a rookies only camp extremely important. Not only is LeRibeus learning a new blocking system, but Redskins coaches are asking him to learn both guard positions, as well as develop as possibly the team's long term center option (which is a new position for him).
Another point about learning these new schemes is the fact that Washington is tweaking their playbook to best accommodate Griffin's strengths and favorite type of plays. They are going to tailor their offense to putting Griffin in the best possible position to succeed. LeRibeus won't have any sort of similar considerations, and will have to learn the offense that isn't most comfortable to him, but one that is best overall.
In addition to the sheer difference in positions, people will also point to the natural talent level of Griffin over LeRibeus, as why Griffin's absence is more concerning. But on the flip side that natural talent also gives Griffin quite a few advantages.
Griffin does have a major talent advantage, and while of course you want to see the Redskins have the most time to develop it and mold it into a Franchise Quarterback, his talent should help him overcome minor bumps in the road easier. Griffin was an undisputed top level prospect in this draft class, LeRibeus on the other hand was considered a reach by many draft pundits, who thought he should have gone 50-75 picks later.
That talent/status level also comes into play when looking forward. Griffin is the Redskins starting quarterback, and as such will be getting first team reps throughout training camp, preseason, and the regular season. LeRibeus is not only not a starter, but he's not even the primary back-up (during Mini-camp Tyler Polumbus played with the first team in place of Kory Lichtensteiger). He won't be getting the same level of reps, and will be splitting time between two positions. It's even more troubling for a player like LeRibeus who missed all of his junior season, and could use the extra work now.
The status argument favors Griffin in more crucial way, and that is that his leash is simply far longer than LeRibeus's. If Griffin struggles in camp or during the season, the Redskins will chalk it up to growing pains and it will have little impact to his long term consideration. But if say LeRibeus were to struggle if given a starting opportunity due to injury (or even from a back-up role), he will be quickly replaced and passed up on the depth chart. And going forward his outlook will be considerably bleaker.
It is that outlook, which makes LeRibeus possibly have a greater negative impact than say Griffin. Because if due to the reasons listed above, LeRibeus doesn't develop and becomes a bust it could have a lasting sting on the Redskins. Between a poor history of retaining premium picks, a cap penalty that will limit free agent additions, and the high cost given up to trade for Robert Griffin, the Redskins margin for error is extremely small. They need their remaining picks to succeed at a high rate, and can't afford to have a high third rounder not produce.
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