First and Foremost, Offensive line is about the size. Standing at just under 6'6, and weighing over 300 pounds, Joe Staley's got that. But also, especially at the tackle position, footwork is key. Joe Staley hasn't been a LT for long, he was a TE for most his college career, but then he was turned into a LT. So being a former TE, he has quicker feet than most LT's do.
now he wasn't phenomenal by any means at LT this year, but in the draft, its not about what you were, its about what you MIGHT BECOME.
The reason people are so high on Staley is very simple, he has the potential to be just as good a LT as Joe Thomas, it's just gonna take some more time for Staley to really learn the position and add on some more muscle. His potential far surpasses Ugohs, and even Levi Browns as well. Because scouts have really seen everything that Brown and Ugoh are capable of, but Staleys potential has still yet to be tapped.