If you could control the tank completely from the gunner or commanders positions, no one would EVER use the drivers position... which would detract from the realism of driving the tank. Being able to turn the tank from other positions is a bonus IMO, and makes fighting on the move possible.
Now this is just speculation, but I doubt that the binoculars used by the commander would have been nearly as powerful as the optics for the main gun... and they dont need to be. All the pintle gun spot needs to do is detect movement, or the shape of a target in the distance, then it falls to the gunner to track to that bearing, confirm target ID, range, and fire. A good GV'er will be able to spot another GV within firing range from the pintle spot, even if he cant tell what it is.
Shooting on the move in WW2 era tanks is definitely going to be difficult at best. There were no computer controlled, gyroscopic stabilizers for the main gun back then, and you feel every little bump you drive over. This gets transferred to the main gun and multiplied when you are zoomed in at long range... every movement of the gun is amplified by the same zoom factor you are using over distance. So with this in mind, the GV that is set up in a defensive position, and sitting still with engine off, most certainly has a huge advantage over the moving tank.
As for knowing the position of the main turret, I dont usually have an issue with it. I also line up the turret by noting the direction the scenery is moving as I look through the sight. And if you are sitting still, it really doesnt matter unless you want to turn and point your heavier front armor to the enemy, in which case you would have to reline up your turret anyway. Not all tanks (even those of the same type) had position indicators. Some used markings on the inside of the turret and main hull which just had to be lined up and read off by the loader. Although, a simple, and single way to just command the turret to return to forward position (not instantly... but at regular speed) is definitely something I am in favor if.