We're talking about a different animal here. Kennedy isn't Ali Marpet. Marpet was the best lineman to ever come out of Hobart and one of the best D3 OL in history. 3x First Team All-Conference, All-American.
Kennedy is a second team type. If he were a pro already, he probably would have gone pro instead of being a grad transfer.
I do agree...OL you can find anywhere...but its different when you find these guys and they go to the NFL. Once they go to the NFL, they can work - essentially - unlimited hours to get their body in shape, learn a playbook, etc. Pro game also builds a lot of OL from scratch. You always hear, around camp time, the NFL coaches complaining about the lack of ready made OL for the league and the amount of coaching and refinement a lot of players need.