Fizz is currently better than being Jax than Jax is
Fizz Q > Jax Q because it applies on hits Fizz W ~ Jax W, Fizz's giving %hp damage probably is better though Fizz's invulnerability is way better than Jax's and gives him another gap closer Fizz's R can't really be compared to Jax's R since they do different things
Just build Trinity + bork on Fizz and never play Jax again tbh
Sources: LCS, LCK