The biggest reason that ADCs are OP AF atm is that they dont have to change builds.

If you play any other class, you have to change your build or at least your build order depending on the enemy team composition in a game and how strong you are compared to the enemies fed champs.

If you are a tank you can't just stack armor against a team where your lane opponent and the mid laner are mages and the enemy jungler is a tank. You have to buy some health and MR and then go into armor in the mid game. Mid laners against an AD assassin will delay a build to pick up 2 cloth armors. Bruisers will delay BC or TF to get some early MR against a mage or tank, or tabis and a cloth armor against an AD threat.

But ADCs in every game have the same build and the same build order. If you are a crit ADC you go into a zeal item, then finish IE and get another zeal item. Then you pick up a item or a defensive item at your leisure. That choice of items is your only expression in terms of build diversity. If you are Ashe/Xayah, you get before IE, which becomes your third item instead of a double zeal.

If you are an AS on-hit ADC, you go rageblade into hurricane into wits into bork.

ADCs, unlike other classes do not have to adapt based upon the game. A year ago when the memes where "ADCs in 2017" it was because they were all rushing crit, which actually had a cost on it at the time, and lethality (which had been overbuffed) was beating the crit users in lane. (because adcs dont build any armor. They dont adapt builds) So instead of nerfing lethality and ADCs adapting to changes where they might have to pick up an early cloth armor to combat lethality, Riot just buffed crit itemization. Which was the worst thing they could have done. Because when crit itemization is strong it takes all its competition out. By getting 3 crit items you can deal damage to EVERYONE.

If against a strong tank, who has picked up a bunch of kills and is stacking health and armor, common sense would be to build a bork and a LW item, (not even completed, LW alone gives 35% bonus armor pen, the same as the upgrades versions. For 1300g) but instead ADC players just whine about how tanks are unkillable in the early-mid games. Which is when tanks are meant to be strong and ADCs haven't hit their stride yet. Because they are buidling crit. Which scales.

If you are against a strong AP threat, maybe an early hexdrinker for safety? No, you need crit items.

ADCs aren't like other classes, they are literally left with cookie cutter builds that do not vary game to game, yet scale harder than anyone, and if a class builds to become more powerful at a certain point in the game than them Riot nerfs them and their items.