Crit chance Max
Simple. Crits allow an ADC to have consistent damage that is double what it normally would be. Their damage already scales quadratically, so the crit damage also scales quadratically and it's just a huge mess. This is most likely the reason tank stats are useless and why I have to buy thornmail if I want to tank. So what I propose is simple.
Max Crit chance at 40%
Then we can buff gangpank and Garen.