LEAGUE NEED ITEMS RESTRICTION

Hello my name is bill.I have been playing league for 2 years and i noticed something very distubing and unfair not only to me but to my fellow teammates.I know you are trying to be creative with items but when i see an assasin go tank its blows my mind it gives him an enormous advantage over normal builds and its killing the game balance.I was wonndering if you can fix a system which for example when someone goes support he is only allowed to take suupport item or the assasin example i was referring to.Please do something so we will have a healthier and more balaced rift