It's interesting.  By definition there can only be five top-5 left tackles in the NFL.  Yet, every draft class there are multiple tackles that are described as being "potential pro-bowl", "potential elite", and "potential top-5!" left tackles.

Let's take a trip down the memory lane of the last 4 drafts to see what happened when the scouts moved on to the next draft class and the players actually had to play in the NFL.

Common sense draftology says that offensive tackles are excellent first-round picks because they have a low rate of busting.  Tyron Smith is the "best" OT so he's extremely unlikely to bust.  A good, safe pick.  Well, let's see if history agrees with this assessment.

As Tyron Smith would be taken at #9 I am comparing him to OTs taken in the top-15 picks.  Furthermore, since Dallas' Super Bowl window appears to be open for 4 years, he needs to make an impact in that time.  So we are looking at tackles drafted since 2007.  How many other tackles have reached their "potential"?

In the 2007, 2008, 2009, and 2010 NFL drafts there have been a total of 12 tackles taken in the top-15.

Lived up to the grade:  These tackles have lived up to their billing of being able to take over the left tackle position and play at a high level

Joe Thomas - 2007

Jake Long - 2008

Ryan Clady - 2008

Russell Okung - 2010

Dissapointments and Busts:  These players have underwhlemed on the right side or have failed playing left tackle. 

Levi Brown - 2007

Chris Williams - 2008

Branden Albert - 2008

Andre Smith - 2009

Jason Smith - 2009

Eugene Monroe - 2009

Anthony Davis - 2010

Incomplete

Trent Williams - opinions are mixed in Washington if Trent can grow to excel on the left side or if they need a new OT to handle the job.  I give him an incomplete after his rookie year.

Analysis

So here we see that the "safe" top-15 OT is not quite as safe as it appears.  Only 1/3rd of top-15 tackles have been able to successfully handle the duties of a LT in the NFL.  The other 2/3rds have failed.  Guys like Eugene Monroe and Levi Brown were given the opportunity to play LT and got their QBs killed.  Others like Anthony Davis and Andre Smith have been below-average even at right tackle.

What we see is that top-15 tackles such as Tyron Smith are about 1/3rd likely to be successful LTs, 1/3rd likely to be solid but forgettable RTs, and 1/3rd likely to bust out completely and be useless.

When you hear hype about how much "upside" Tyron Smith has, remember that all the same things were said about every one of these 12 tackles taken in the last 4 years.  For 2/3rds of them it was nothing more than blowing smoke up the GM's butt.  It's a cautionary tale that says most things that glitter are not gold.