Well, lots of people disagree with you. He might not be the fastest running back in the world, but he's plenty fast. As someone else posted, he's recorded good 40 times. And on top of that, he shows good speed on his highlights. He's also a 5-star or high 4-star to all of the recruiting sites, IIRC.
And while you insist that he's more likely to be a linebacker, I'd say it's pretty rare to find a high Division I guy playing linebacker at 5'11". I know it happens sometimes, but not very often.