idont think you understand the term hard counter
no matter how fed you are, if lulu ults and shields your target, it isnt going to die, if it uses any of those items or summoners, probably not going to die. stopping his ult from proccing does tremendous damage to burst and usefulness(and when you thing about it the ADC SHOULD have cleanse, and the APC SHOULD have zhonyas, in basicly all situations, especiallly against zed)
just because he can kill an unprotected target instantly when hes fed doesnt mean hes op. so many other champions can have greater impacts on the game,even when theyre not that far aahead (ie jax and irelia, both of whom can kill carries just as fast and tank for their team at the same time)