To be honest I think the way to fix Jax is to keep his damage the same but add a small delay to his E stun so that it can be outplayed. The way he can stun on demand means it's just way too easy for him to all in, because if you flash out of his E, he can flash on you and stun, with the small delay there'd be an opportunity to flash the stun to get away, but he can still flash after you before the end of the delay if he's quick enough, in that scenario. If you have flash advantage it also means something.
It also means he can't do his short trade of Q auto W E and walk away for free, because he could be run down as there would be less fear of being stunned in his minion wave.
It's the same reason Galio's flash taunt is so OP because it's on demand and there's little counterplay.