Some college three point shooters who hit their shots at only an average or above average rate, simply don't translate to the farther out three point line and the speed with which defenders close out on them. His shooting woes have nothing to with his size, it's just he wasn't a great three point shooter in college at a closer ranged shot and he can't adjust to the NBA game.
Fultz isn't the comparison. R.J. Hunter is. Edwards game just doesn't translate to NBA success, much like Hunter. I doubt Edwards finishes this year in Boston.