Browns are 4th in the league in terms of how many points per game they give up and 6th in total points.
That's a fairly important factor as to why they are 6-3. Granted, they do give up a good amount of yards, but they've done a good job of not giving up points.
Some quick back of the envelope numbers:
Shanahan Averages since 2010: Total Yards: 11.6, Pass Yds: 13.8, Rush Yds: 14.2 & Total Points: 17.8
Jets Averages since 2010: Total Yds: 21.4, Pass Yds: 28.6, Rush Yds: 9.2 & Total Points: 22
Obviously he's much better at creating an offense that can get yards through the passing game, which no doubt is extremely important in today's NFL, but in terms of rushing and points, its marginal. Over the last 5 seasons Shanahan coached offenses have scored approximately 1.8 more ppg than the Jets. Considering how awful our offenses have been the past few years (which really skew the numbers IMO) I'd like to see stronger numbers in that area. Especially when you consider he is an offensive guy and I'm comparing him to a defensive minded team (in theory) who has been utterly inept on the offensive side of the ball. I don't see a top 3 head coach candidate. Maybe in the future, but now? That's a difficult proposition for me to accept.
Kid has the pedigree and bloodline for it, so I'm sure he'll get his opportunities in the near future. Just don't see it happening in the next year.
But I'm open minded and a persuasive argument might sway me.