I'm sorry, but Brian Hill should not be included in the same category as Smith and Alexander.
Alexander didn't leave early because he was given a high grade by scouts. He left because his family needed the money. Found an old tweet from Gags that Alexander said he was told: "With my athleticism and talent I have I have the potential to
work myself up to being drafted." Smith was confident in showcasing his ability at the combine. However, that opportunity never came. He never consulted DC, who
said he would've told Smith to stay in school. Maybe it was bad luck on his part, but I also don't the spread didn't do him any favors in showcasing his arm talent, or maybe did a good job of hiding his lack of arm talent.
On the other hand, Brian Hill has put up MAJOR numbers in a system that easily translates to the next level. There's no question about if he could run at the next level. Honestly, the biggest question about him will be his ability to pass protect. But that's not an issue limited to Hill at the RB position, a lot of RBs struggle there.
That being said, I hope he stays through his senior season. One of the biggest reasons being, the offseason predraft circuit is a great venue to showcase his running ability. Underclassmen are ineligible for the East-West Shrine Game and Senior Bowl, meaning his draft stock would be a lot on his pro day and the Combine (if invited).