But in regards to the part I quoted, put the debate this way:
Durant might go down as the best combo 2/3 ever, second best perimeter scorer ever.
Wall has the ability to go down as the best pure point guard ever.
Now thinking about it like that, which one would you rather take? I think positional importance has to figure strongly into the equation. Perimeter scorers who can give you 24+ points a game are a dime a dozen. There's never been another player like Durant before, but you can get a guy who'll give you close production nearly every single year. PG and C are the two most valuable positions you can build around and there are swarms of good 2s and 3s in the league right now. If I were building a team with the ability to choose from every player in NBA history, my first pick would be Kareem and not Jordan or Bird.
Point guards with no weaknesses and freakish athletic gifts (speed, length) like Wall are extremely rare. Also factor in Wall's youth, precociousness, and leadership skills. He's captaining a team as a 20 year old rookie, two years removed from high school. I think he's the most desirable building block in the league outside of Howard.