Fizz's E ISN'T THAT BAD.
Untargetability doesn't mean invulnerability. He's countered by abilities that don't use projectiles, and DoT abilities. I really don't play Fizz anymore but if I did, and they nerfed his E to the point where it didn't even give him untargetability, he'd be pretty garbage considering you could then interrupt his E AND his Q. One CC ability while he's going to Q you and he'd be dead.