Master player take on current issues with ADC itemization + Don't expect changes until S15
The reason most ADCs feel bad or underwhelming is itemization. Ranged AD itemization got nerf after nerf after after nerf following the 14.10 changes (which I think was terrible but not the topic) mainly because of proplay: Fleet nerf, Absorb Life nerf, DBlade nerf, Botrk, Kraken and Shieldbow nerfs for ranged, I could go on and on.
Not only that, but the items that got nerfed the hardest in 14.19 were the ones built by ranged AD characters: even more nerfs to Botrk making it borderline a troll item, Wits End? It was already an underwhelming item to begin with and its on-hit damage was cut in almost half, IE and LDR nerfed to the ground, and Shieldbow well, it wasn't nerfed because it was already shit.
In compensation, Collector is now a pretty good item, so is ER for the few champions that can use it well, aaaand that's about it. Yun Tal is finally somewhat decent but I'm sorry, it has one too many weaknesses: either make it give crit without having to stack or give it a better buildpath. It looks good in theory/once completed, but that's not the reality of soloQ. Oh and we also got LT, which is okay but nothing to write home about (don't compare it to old LT if you're prone to depression).
Now, in comparisson to other classes, ADC itemization sucks, because tanks and mages barely got nerfed, and bruisers lost some damage but in return thet got so much health, ending up in a better spot than I initially thought. Btw I also thought Botrk would be great since a ton of bruiser items got extra health but Riot thought otherwise and slapped us with the 5% max HP on ranged. Not even Twitch is building this item anymore ffs
This is why the game feels like mage city right now (not talking about botlane specifically) , not only do they have better and cheaper items, their components are also better (reminder that we lost old Noonquiver in favor of the new one, which is beyond bad, and we have new items like ELASTIC SLINGSHOT and Hearthbound Axe which are mediocre at best, meanwhile they have things like Hextech Alternator or Lost Chapter). The reason why Collector is one of the most built items in the entire game is because is has a decent buildpath that includes Serrated Dirk, that's it. On top of this, bruisers are too tanky and mages deal a lot of damages, but ADCs can barely build any lifesteal anymore (BT no crit=can't build it 2nd or 3rd anymore, Shieldbow no lifesteal, Botrk is beyond bad and Bloodline is another case study). In case your champion is allowed to build some MR, well sucks to be you: Wits End sucks now, so does Maw, and Mercs are 1300 (thirteen hundred) gold, okay. This is why even when you're fed, playing an ADC feels like walking on eggshells (more than usual I mean) because defensive items and runes suck, so 1 mistake is all it takes.
I thought with the new season changes they would tackle some of these issues, but there's nothing relevant on the PBE. My prediction is that once pro play comes, crit ADCs will barely see play (not that on-hit ones are much better, but their buildpaths and items suck less to build and allow for more flexibility and defensive stats), and then Riot will start changing things. You used to be able to play ADCs in mid and top before and look now, they are barely playable because when you are forced to compete with mage and bruiser items, it's really one-sided towards those in terms of tools. This is also why it sucks to occasionally play vs mages botlane nowadays, their items are just better.