A big part of taking Barkley first is stating he's the undeniable best talent in the draft, and believing in your scouting to find those gems in the rough. Snee was a second round pick, Justin Tuck was a fourth, Osi in the second. By that same token, Jacobs was in the 4th and Bradshaw in the 7th (I think these all correct but I could be wrong on them).
You are correct in the value based on dollars, and it's really the most sound argument against Barkley. At the end of the day, have to trust Gettleman that he made the right call. I would've been happy with Barkley, Chubb, or Nelson.