It doesn't seem inconceivable that wearing shoes takes you out of the path of least resistance as compared to some other path, say, the metal-framed shelving you are standing next to. I don't think wearing shoes is any kind of practical way to avoid getting hit by lightning but the 'kilometers of air' argument seems sort of wrongheaded. You don't need to become a more resistant path to ground than a kilometer of air - you just have to be more so than other paths. How long the discharge traveled to form that path doesn't really matter.