Deron is not playing, and you keep somehow missing the point. It's not about what TD does against other players, and it's not about whether or not MDA cares for TD or knows the PG position well...Toney Douglas is not a point guard. He's a shooting guard trying to make the transition, a very tough transition, a transition that most small SGs don't make.
Toney Douglas' position is shooting guard, Toney Douglas' skill-set is best utilized at the shooting guard position, the best place to put Toney Douglas to maximize the talents that he currently possess without trying to "teach" him a new position is shooting guard.
Toney Douglas can naturally get his own shot, when he's trying to run the offense and facilitate...it doesn't look natural. You can see point guard qualities that can be grown and expanded in young players, TD doesn't really show those qualities. Even when he puts up decent assist numbers he still looks like a shooting guard that's passing the ball as opposed to a point guard running the offense.
If he didn't grow up controlling the ball and playing the point, then chances are he doesn't have those qualities in his game. It doesn't matter how much the coach cares for the player, some things can't be taught by another human being...so you roll with what the player has and work with that.