If any other champion tried the same thing they would go oom/ooe much more quickly.
Akali can detonate marks (the majority of her damage and her main play pattern) literally infinitely until the end of time without ever running out of energy. Kennen can ration out his energy so that he never dips below 80%, especially since autoattacks are involved in his primary regeneration mechanic.
Zed, on the other hand, has to toss out his entire kit almost simultaneously to get the benefits of his regeneration mechanic, and unlike Kennen or Akali he only has the opportunity to do this once every 14-18 seconds within a four second window.
Kennen gets back 65, Akali gets back 40-60, Zed gets back 40-80. Zed can get more energy back than his counterparts and his spells cost less. That's my point.
Kennen gets back 25 every time he gets a passive proc, which can happen three times within five seconds if the player is particularly skilled and uses his ultimate effectively. Akali refunds the entire cost of her primary damage ability every time she detonates the mark.
Each of Zed's individual spells cost less, but in order to get the benefit of his regeneration mechanic he has to use them all at the same time. His initial energy investment for the return is far higher than either Akali or Kennen, it's actually on par with Shen.
Akali only needs to spend 60 energy to gain 40 back, whereas Zed has to expend well over half his energy pool to accomplish the same.
You also missed Shen whose combo costs 210 at all ranks and he can only return 40/champion hit if he lands his taunt.
I didn't include Shen because his energy restoration and role in general function very differently from other energy users. He is also widely considered to have overly punishing costs, so he isn't necessarily relevant to this discussion.
- One popular idea is to reduce his waveclear by halving the damage on his e and q to minions.
The damage is already heavily reduced by the innate pass-through mechanics on Q, and E does very mediocre damage until roughly level 8-10. A possible alternative might be to make the pass-through affect minions differently than champions, but it's important to consider burden of knowledge with a change like that.
- Another popular idea is to remove his passive effects on minions to force him to last hit to farm.
This would render his passive almost useless, because he very rarely has time to autoattack his champion target within that health window.
- One change i read was that he could only port back to his shadow on command once, so he couldn't switch back and forth over and over.
- He can switch with his w as much as he wants but can't switch to his ults shadow or vice versa.
I really hope I'm reading this wrong, because if this discussion is based on the assumption Zed can infinitely swap shadows...
Zed can't switch more than once to any of his shadows; he can switch to his W once or to his R once, that's it. Once he switches there's no return.
Maybe the passive on his w is only active if the w is off cd. His w can be used to escape but then the death mark doesn't get the 25% ad boost so it encourages him to stay until the enemy is dead without requiring him to stay until zed is dead. If he uses his w to waveclear then he automatically does less damage to the minions.
To clarify, when his W is available to be cast he would have the boost but not when it's out? This is directly counter-intuitive to the mechanics and pattern of the champion; he's designed to be at his strongest when he can use his W to amplify his damage through multiple casts. It would be a bit of a design conflict for him to lose damage when his main damage amplification ability is in use.
- Make it so he only gets energy return on one of the mimiced casts when he uses his weq combo but raise the amount so he only gets, say, 30/50 energy returned at rank 1/5 instead of 20/40 doubled to 40/80.
Theoretically, this would increase the reward of hitting the much easier E double proc and devalue the benefit of double hitting Q. That amount of energy regeneration may also be disproportionate to the costs and availability of said regen mechanic.
- Remove the energy return on minions so he has to hit his skillshots on enemy champions to get the energy returns.
This would likely make him extremely feast or famine, and run him completely dry on energy almost permanently. He would also basically never land the mimicked E, because it's melee range from two separate characters 550 units apart.
He would also no longer be able to jungle or even really farm at all, let alone split push.
, he has no kill pressure on you IF you can land the silence. Cho Gaht's scalings are so high that you can have kill pressure on him getting a second item 
- you can kill him all game prior to 
.
also counters him pretty hard.
new meta. Jk, but its funny that when he ults you, you can just put your silence on yourself and watch as all he can do is auto attack.
