CD nerf would make Jax reasonable
E and R are both lower CD than most other spells of equal power in early
E at 16 and decreasing with rank and R at a static 80 - his first item also giving 20% CDR
Most key spells on melee carries that are of a similar power will be 20+ seconds until they rank the ability or get CDR ( riposte, wind wall, meditate etc.) on top of being Jax's all in tool
Putting his early down times on par with other champions would be the most reasonable way to address his current power level imo - no late game nerf needed