I think overall spotting works quite well and statistically delivers good results while not being too predictable, but where I have a problem is the most important aspect of tank duels and who has the tactical advantage. After more tests it seems that the size of a tank-target (full hulldown, size of silhouette hitable) has much less influence of being hit, than the factor who moves and who stands still (and therefore usually spots first).
The inaccuracy of the Soviet 122 mm gun seems to be not modelled and therefore doesn't reflect the poor performance of JS-2 and ISU 122 tanks. Their somewhat weaker in-game performance seems to be mostly a result of the slower ROF.
ps: in the meanwhile I have found a great workaround to eliminate the spotting disadvantage of the tank that breaks LOS when he attacks from his hulldown position, but it is an extremely gamey trick and was not practized in reality.