The cases are hardly similar, and a lot of Zed's problems aren't due to the nature of his interactions with champions, but rather the infinite nature of his waveclear. Notably, Zed was not a problem when most mana users could simply outpoke and out clear him, but due to regen nerfs, Zed is now problematic because his energy combined with excellent, safe waveclear is overbearing. Kennen's waveclear pattern is not nearly as strong as Zed's.
The OTHER problem about Zed, which was still present even when he was balanced, is his absolute safety when he engages. Whether or not that should be maintained is debatable, but IMO the waveclear is a bigger problem and the safe engages are just icing on the cake. But notably, Kennen is once again different because the manner of his engage is unsafe - he puts himself into the middle of the enemy team. If the fight starts going against his favor, he WILL die, unlike Zed, even if he has Zhonyas.
You can't build against Zed's waveclear, nor can any of the items you build make him less safe.