It is possible to have everything correct and still get rubbing under load or when there is flex. I have a friend that is a little heavy and he gets a slight drag or rub when turning. Not enough to slow him down but like you said it is frustrating. I tried to adjust it for him, he took it to two shops that have good mechanics and they told him it was flex and there was nothing he could do. Now when he rides my bike there is no rubbing at all. If the wheel is true, the disc is straight, the rim has no play side to side, I would almost think there is not much he can do. Have you tried checking the front shock for flex from side to side?