ZED CHANGES ARE TARGETED AT FRUSTRATION, NOT POWER
Specifically, they are designed to force Zed to be more interactive in lane.
#Q: better trading, worse harass
Double Q does more damage but single Q does less
Imagine you're Xerath, laning vs Zed. He throws out his shadow, hits you with a shuriken, and spams /laugh, because he's standing 2 teemos outside your max Q range. Repeats every 15-20 seconds until you have to base.
Now if he wants to do more than tickle, he has to walk 7 teemos closer to you, in range of all of your abilities.
A straight nerf to Q damage wouldn't work. If you nerf his numbers, his pattern stays exactly the same, he's just weaker. The buff part of this change is what actually changes his pattern; but obviously you can't just buff Zed.
#R: Less free damage
R has a smaller AD ratio but more damage amp
This one's pretty simple. If Zed ults and you outplay him and dodge all his abilities, you deserve to live. With a smaller ratio for just pressing R, Zed actually needs to hit his shit if he wants to kill you.