Crit should be something to surprise you, not to be relied upon to do damage. It should be something that happens by surprise that may win a very close trade or fight. The fact that all adc's rush 70%+ crit chance is stupid, it shouldnt ever breach 40%. There should be a cap. Not to mention we need new ad items that are guns and stuff that say "ranged only" so we can put a lot more ad on them to make up for the lack of crit damage. (kinda). This is the only true way to balance adcs AND keep crit in the game.
ALSO NEEDS TO LOWER THE DAMAGE RECIEVED FROM CRIT to like 150%.
If it says ranged only, then the abnormal amount of ad cant be abused by bruisers, etc. NOT TO MENTION, since they wont be doing abnormal damage, they can get some very LIMITED defensive stats on these ranged items so they dont insta die.
They basically become ranged fighters that are half as squishy as regular melee fighters, but dont get insta-blown up in teamfights unless focused. What sets them apart from melee fighters is that fact they have better seiging potential.
I know what you are going to say next. "What about gnar and urgot? They Will Become OP" Then just rework them so that their autos count as ranged melee. This makes sense since gnar's true form is melee, and urgot has a very close auto range, albeit still ranged.
I think this would let adc's still do decent damage, keep their importance for seiging, but take away from the ridiculous amount of teamfight kill potential the give, where teamfights last seconds.