This are the facts as i understand them
a champion that you can counter itemize with only one item is crap ... thats a bad side of zed
but the gameplay that this creates due to the sheer extend this item couters him is also crap ... thats a bad side of this ballance
now lets look at how zed or should i say riot handles that
a)since zed's ult is removable and counter items are easy to obtain on top of being good ... zed gets additional power ... which enforces the items to be bought in order to counter zed ... if you wont buy them you have no chance ...
It is a shitty loop of zed being compensated for being handicapped which makes it so enemies need to handicap zed
b)Since items wreck zed hard ... he usually finds himself unable to function in teamfights ... since his targets are immune to him
Let me say this clearly here ... the way that riot handled this is complete shit for both sides
enemies are forced to build accordingly to enemy champion under a threat of losing a game
you can counterbuild a mage in loads of ways that will suit you ... you always have choices ... countering zed has none, you are forced into one specific item
While zed plays a game of "i need to destroy everyone before i will be removed from this game"
overall there is bad gameplay given to both sides just because zed's ult is removable
also THIS IS HIS ULTIMATE ... THIS SHOULDNT BE REMOVABLE WITH A BUTTON PRESS