Half the problem with season 6
is that ADCs are so strong right now that you are seeing 2 of them per team at all levels of play in many games. ADCs can flex into mid, top, and jungle. They dominate at all stages of the game. They are no longer weak early, but have unparalleled strength late game, across the board.
If an ADC gets fed, the game may as well be over. Tanks can't tank them anymore without devoting 4 items to them. The game is, right now, all about them, and anyone who doesn't play them has been left behind. They were strong before they were massively buffed. They were fine before randuins and and frozen heart got nerfed, and before APs got pushed to near irrelevance by the blanket nerfs to their itemization in addition to buffs to the two biggest MR items.
Seeing 4 ADCs in an LCS game isn't interesting. I just roll my eyes, because I know that the reason it works is because they're just too strong; because they're crowding out diversity by being far more prevalently picked. Maybe if something other than and ADC could go bot without being insanely overpowered like mordekaiser, it'd be ok, but as it is now, that's not the case.