Stockton had the same issues in Utah. I often felt if he wanted to he could've been a 20 point scorer if he really wanted to.
I wasn't really trying to make that comparison, because Stockton was a very good offensive player who was too passive some times. Marshall is a sub-par offensive player who is too passive, which makes him terrible offensively.
It's hard for someone to improve offensively if they don't work on it in the game, and I feel like Marshall is finally starting to do that.