Champion Diversity has gone up, but Build Diversity has gone down

That's the biggest problem in the game at the moment. Its not the "OP" Champions that are the problem, its the ITEMS that currently exist in the game. This is why a lot of assassins are able to get away with building tank. Riot continually miss the mark by nerfing the problem champion (e.g. ) and not the ITEMS in general (e.g. ) which are way too strong.

That is the problem, there is a complete lack of build diversity because some items are just flat out BETTER then other items and games are so objective critical at the moment that you really do not get time to experiment with different champions while you do this. Assassin Tanks are simply symptoms of a bigger a problem, which is the lack of Build Diversity in this game.

Pretty much everyone will build the same items on the same champion, every game and this leads to a boring experience where every game of League feels the same (something that Riot is against) and although Riot has started to tackle problems in champion diversity (with reworks etc), they have completely failed to address the problem in build diversity and the balance between items within the game.