This has been my problem as well. I can destroy with Steph Curry, especially after giving him a realistic quick release.
I've been playing around with on ball defense at 65 and defense awareness at 85. It does kill a lot of the fluidity of the penetration game but maybe it's not that unrealistic. The game doesn't seem to give you as much of an advantage driving when the D plays tight though. In fact it seems worse at times. There should be separate sliders for how well the CPU contests or plays tight as well as how well the CPU defends and reacts to drives. They shouldn't be linked as one slider.
What should happen is the AI adjusting to play extremely tight on Steph at all times, even off ball. In fact, it should just do that from the start given his high 3pt, off the dribble ability, lack of speed, and high 3 pt tendency. I don't think the CPU knows how to adjust for individual players apart from after they heat up and throwing double teams at them. It then let's off them after awhile and you can resume shooting the lights out again. It also doesn't cross match defenders and put a better/longer defender on your star if it makes sense like Curry saw throughout not the Spurs and Nuggets series.
Maybe I also need to lower help defense so defenders don't sag on him off ball?