I figured out every balance problem currently
The hybrid items.
The juggernaught update brought more items that gave ad and tank, the mage update brought the hextechs which changed a lot of mana items for more tankier ap items. The ADC update brought and changed the armor pen items.
If you look closely every one of these items are what people complain about. Tanks have items that make them really tanky AND deal damage (
, 
, 
), AD damage dealers have items to make them more safe, and be tanky (
) OR just 2 to 3 shot any squishy 
, and mages have multiple items that give hp more burst/more safety, and health 
These Items are one of the main reasons why the game is in such an unbalanced state right now. Giving people the choice of doing 2 builds at once is the problem.
