Fizz is also the optimal champion for countering AP Mids who have no sustain. Even with the healing reduction, heavy sustainers like Swain can just un-do the wearing down that Fizz does to him.
This also brings me to Ryze. Many people believe the Ryze hard-counters Fizz but Fizz beats Ryze at level 2 so you can actually snowball out of control with Fizz if you capitilise on killing Ryze at that level. So then when Ryze enters "The Ryze Zone" you are already out of laning phase and are one-shotting the ad carry in team fights.