Dribbling off his foot isn't a case of him having a low basketball IQ. It's a case of him needing to improve upon his basketball handling skills.
No matter how long you repeat the mantra that DC has a low basketball IQ it still will never change the reality of who he is as a basketball player.
Night in and night out DC shows he understands the game of basketball game well by attempting to run PnR's, find his big men in the post, and attempting to break down the defense and find open shooters/cutters. It doesn't matter how many mistakes he makes, that doesn't suddenly mean he has a low basketball IQ. That might mean he plays a little out of control, or maybe he plays careless... There could be a number of issues that cause him to make mistakes.
I'd say he is like most point guards that have ever played the game in the last 50 years and that is they usually take longer than two years to turn into a solid starter. But that's just me.