The issue is that the game at the moment revolves around ADC being a require thing. It's so cemented into the game that the role has pulled in more power.
Their damage is borderline burst at mid game, and late game, their damage matches AP champions in burst but it's more reliable. More importantly, they are still the best objective takers, as well as tank busters.
Riot jokingly said that ADC should probably be considered mid game champions while AP should be moved and buffed to be better late game because their damage isn't always guaranteed. The same issue for the most part plagues the other roles from truly becoming broken. Assassins without Dusk aren't good. Majority of assassins are gated by delays
Tanks aren't OP. Their winrates are pretty low but they are effective in team fights because they enable broken champions from doing what they need to... IE ADC getting free hits while you are CC'ed
That's just me.