Zed's transporting between shadows shouldn't make him untargetable and should be slower

I am getting the feeling that you do not play Zed often.

Two things:

1. Zed's shadow makes him as "untargetable" as flash does. He literally dodges the skill shots aimed at him by porting somewhere else, unlike Fizz or Vlad whom the projectile will just pass through. If a point and click ability/AA is used on Zed and he activates his W, said spell will follow him until it lands. The only time Zed's shadows make him invulnerable to anything is when he is turret diving, and that is only if he shadows out of the range to avoid a turret shot, similar to a champion dashing/walking out.

2. Zed's W shadow already have a throwing and activation delay. Play Zed against LB or vice versa, and you will see that LB's Distortion, which is mechanically similar, is a lot faster than living shadow. However, once the shadow lands, Zed can switch places with it instantly anytime he wants with 4 seconds as long as he is within ~1000 range, but he cannot move the shadow, so he will always switch the same place. His ult on the other hand has a much shorter delay, which may be what you were referring to, but hey, it is an ultimate after all.

I am not disagreeing with you that Zed has extremely low risk for an assassin; however, a better change would be to make him unable to port back to his ultimate shadow with several conditions.