ADC main here, what you describe isn't the issue.
in a straight 1 v 1. for most of the early and mid game, an adc should probably lose to a tank. that's just how its always been.
late game even, unless that adc has his LDR, a BT, and 70% + crit with a ton of AD, he probably still shouldn't be able to deal with a tank in a 1 v 1 especially if tank has a stun or ultimate up.
where the issue is right now is in team fights. ADCs are a class that has the highest dps, but they have almost non existent dps for most of the game which is a bad feeling. in team fights you can position well and wail on the tank hitting your front line, but it doesnt matter he's eventually going to kill your front line and you've barely gotten through 1/5 of their health bar at best.
tanks deal too much damage early in the game. its a fundamental design problem though that I don't know if you can fix by just "nerfing tanks damage". if you nerf tanks base damages you have problems late game where they are already able to be shredded.
personally I want to see a world where ADCs have a more steady power curve and Tanks are actually tanky in the late game. Right now its a weird curve where tanks are gods in the mid game and get melted late game. and adcs are basically a caster minion for 35 minutes then become gods as well. the thing is I'm not sure how you do this.
if you gut base damage you have to give tanks a scaling source of damage of some kind while still allowing them to build damage? I would personally like for tanks to deal less damage but be TANKIER in the late game. so maybe weaken base damage, but buff their scaling stats signficantly on all melee champs. this is not something that will be fixed over night though. they can't just fix this in a patch or two. this is a fundamental design flaw with marksman and how they interact with tanks.