If we are talking pure upside, I am not sure how much of a stretch a slightly worse shooting Danny Granger is. Similar build and athleticism, similar skillset. Granger is a slightly better perimeter shooter, bug Green is very good from midrange.
Otherwise, they are very similar. Solid handle, good BBIQ, solid defense, good rebounding (for SF), ability to finish at the basket, ability to post up smaller opponents.
I think if Green was given a similar chance as Granger to be "the man", he would be able to be at least somewhat comparable.