Not sure its adc's that need the attention as much as it is the items they build. Especially during laning phase.
The second someone builds lethality, they go from doing 10-15% of your health in a trade to doing 50-60% of your health in trade, all for what...1100 gold?
Compare that to when a laner picks up a BF sword. You go from doing 10-15% to doing 25-30% in a quick trade. For MORE gold.
And yeah, ok, lethality falls off once the armor items come through, sure. But by then, the champ is 3-0, 4-0 and has the money to stack lethality (Which for some reason also means cooldown reduction? Why?) Which makes the armor less valuable, and honestly it doesnt matter because anyone who builds lethality isn't going to be trying to attack the front line tanks and bruisers anyway. They're gonna be trying to one-shot the squishies. So armor is a non-factor.
So lets say the adc didn't build lethality, they went with a different build entirely. The two popular ones right now are guinsoo's/BORK/runaan's and IE/RFC/Shiv.
Crit has been broken for quite some time now, putting up numbers that would kill a champion even through 200+ armor in 2-3 autos. Crit chance needs to be capped somewhere between 60-85%. 100% crit should not be a thing. Especially when the items that give you 100% crit synergize so well with each other. If you're going to get 100% crit, there should be a drawback, and there currently isn't. Especially if you're Yasuo.
Guinsoo's/Bork takes a while to scale up, and is probably the most "balanced" of all the adc builds, because it provides a meaningful window of counterplay. Regardless, once the build is complete, you don't even have to fully stack the Guinsoo's before you're 1-2 shotting everyone. Add Runaan's into the mix for the AoE damage, and you've got a pretty cancerous situation on your hands where you HAVE to focus down a single member of the team fight, or you all die. Heaven forbid there's another competent member on the team that also needs attention.
With the current build paths for adc's and the ludicrous damage they put out, you often find yourself in the situation where "If we focus the adc, this other champion kills us all, but if we focus that champion, the adc kills us all." and you have no viable strategy to win a fight. You're damned if you do, and damned if you don't.
Add a couple champs with shields, heals, or peel, and it quickly turns into a situation where there's just no good option, and you lose the game. As it stands right now, the game is a ticking timebomb for which ADC can get fed first. Whoever has the fed ADC wins the game, period. There's no meaningful way to catch up. There's no meaningful way to come back.