Bruh are you delusional or something, the previous Zed "Q" changes were nerfs to his laning (-10% dmg to Q on 2nd target) so you cant harass with Q properly anymore , they just increased the dmg if you 1v1 him in the jungle/river or without any minion present(or anyone whatsoever which is almost never after the minute 15 mark) , also his team fighting got - 30% dmg hit on the Q(if you use R+W), don't say Zed got buffed, people like you trigger me a lot, you do not even comprehend the changes that happened to a champion. And this "buff" on the pbe right now is not even a buff, they're just reverting it how it was last patch.
Zed
Razor Shuriken (Q)
secondary damage AD ratio increased from 45% to 54%
secondary damage increased from 40/57/75/92/110 to 48/69/90/110/132
-And if you want to talk about Zed vs Rengar, Rengar is perfectly viable with any build you go, while Zed has no other options , he must go Duskblade and Electrocute, because if you don't you will do less damage than a Soraka, Rengar can go Full crit with Dark Harvest or Predator or even now conqueror and still 1hit kill Adc's be real please, Rengar on top of that has Stealth. Also lets not forget his Q is a basic, and its borderline impossible to dodge, while Zed relies on Skillshots.
Please dude.
PS: The low winrate on Rengar is because people dont know how to play him and they end up feeding, Rengar is borderline OP right now , (Rengar+Zed+Talon main here btw)