Those big draft boards are not always right with certain picks, and are usually based on numbers and potential on paper alone. Semi show's a great a great work ethic, is well spoken, and was an all-academic for his conference while carrying his team. At the combine he showed elite athleticism among prospects of similair size, yet weighing much more and while having an impressive 5.5% body fat percentage.
My theory for his bad defence comes to him being a late bloomer and his redshirt year. Not being utilized at Duke led him to transfer to SMU after 2 years. He had a year of inelegibility to play, so he red-shirted. The hardest thing to learn outside of game time and experience is defense, in my opinion. Thats why he had a break out season, improving in all facets, but had lack luster defense. The guy has a great work ethic and it shows in his offense and physique, but I think you give him a chance to improve his defense through more in game experience and help from coach's at the next level.