You know why Fizz is so terrible to play against?
In truth, it's not his mobility. Its 2 things.
1: Some of his passive statistics, and this is specifically for fizz
2: the power he can pull out without building much damage. (this relates to alot of assassins, looking at you zed)
Aight, for point 1. Fizz has so many things that are going for him that are perfect for an assassin, or any melee in general. He has 0 unit collision, a high auto range for a melee, and a high movespeed. Now most have one or the other, but all 3 on 1 champ is excessive
For point 2. Fizz's kit and its ratios make it so that he can pull an impressive amount of damage, with minimal ap. Most of the time, he can kill you in 1 combo at level 6 with nothing but a sheen (which gives no ap) and a dorans ring. Now this is a problem for many assassins as they are supposed to be weak without items, but destroy when they can get farmed up. By having assassins who can do this kind of damage without needing to farm up, mages are made obsolete as they just can't compete

or
: Suus non meus mendum! Mea custodit , sicut de agente.
/
counter Fizz Ultimate.
.