I'm not sure about that. He seems to get to spots where he can definitely make the shots he is given. I agree about frustration showing in his game, as especially when we fall behind by a lot he starts making more mental errors and probably his shooting percentages dip as well.
Last game he started off terrific with few assists in the first few minutes and he made a contested 20 ft pull up. I dont think Spurs really did anything to counter him at any point, but despite hitting that tough first shot and having a good start he still missed all his 3 point attempts including one which was essentially a practice shot with absolutely no one coming for him:
1. Uncontested pull up off a screen, true, hard back iron
2. Wide open transition jumper, true, hard back iron
3. Wide open spot up corner 3, true, hard front iron
4. Slightly contested step back, (maybe) true, grazed front iron (almost air ball)