I'm more afraid of a well built Master Yi, but that's probably because I'm primarily Kassadin and THE SLOW IT DOES NOTHING OMIGOD *flash* *rift walk* phew.. should've silenced him first.
Don't have that problem with jax
To be more on topic though, don't think Jax is OP, strong yes, but not OP. Especially with the addition of these 3 new characters and their miriad of disables (blitzcrank im looking at you o_O), as with all melee DPS if the disabled enough or focus fired (if needed) they just whither.
And he *did* just get the nerfbat, poor ol' Jax