Zed being encouraged into tunneling on the ADC is a good thing.
Part of why Zed has been so obnoxiously frustrating is because he's really difficult to predict. This change will make the ADC such a juicy target it will be hard for any zed player to resist, so that can be used against him. It's the exact same thing as Lee Sin, you let them land the Q on you while you're under tower, and because no Lee Sin player can resist not try-hard showing off, they all take it and get CCd in the face and bursted.
Same theory can be applied.