Whatever Happened To Traditional Team Comps?

The entire team is assassins.. Like that is actually a healthy comp.. Sure if you have a bunch of solo players that play great by themselves, then you might be able to pull it off. But more than likely it will be a disaster. Unless you are playing against the really bad players that just can't get it right. Whatever happened to tank/fighter up top, ap mid, fighter/assassin jungle, with ADC marksman and Heavy Support? Like that is somewhat healthy Comp. But all I see now is Assassin top/mid/jungle/support with an ADC that might as well be an assassin since they aren't good for much else besides damage.

Why the constant pull towards to assassins when Tanks are supposedly the powerhouse? I mean, everyone wants them nerfed to the grave cuz they are to strong right?