Counterbuild is not the same as Counterplay. Counterplay is listed as one of two things; Possibility to respond and Clearness of whats happening.
This is where i'm conflicted with Zed. He does have to possibility to respond I.E stuns, you know where he is going to be and yes, Zhoynas. He also is clear in what he's about to do I.E his ult has a HUGE X and his shadows are of clear visibility.
Counterbuild is like buying Penetration to kill armor, MR to counter AP, or like ya said, Buying Zhoynas or QSS. But let's think abot it like this. Imagine a world where QSS and Zhoynas don't exist. Zeds would reign over every mid laner or adc.
Meanwhile people like Lissandra or... other zed counter would be their only solution. As much as counters are great and all, this doesn't work as well in blindpick or TB and would probably force people to either Main these counters or make Zed a 100% ban pick in any form of Draft.
What annoys people is that he can be really safe to play as, like the OP's shadow in, shadow out, and see if kill resolves with the extra damage, let alone it being seemingly impossible to rush Zhoyna's pre-six. And QSS as much as it is great killing the extra damage, is seemingly useless otherwise since all it gives is MR.
It essentially is the tunnel vision: at the end is a zhoyna's and chasing you down said tunnel is a Zed. Only way to go is towards the Zhoyna and salvation or getting merc'd by Zed. A lot people or champs don't got the choice to break through the wall.