From several patch jax has been continuely nerfed (e.g. his Q and ult passive dmg), but compare to another old champion like renek, nasus and darius they had been buffed from the nearest patch.
How ever even mordkaiser been reworked with new feature and play style but jax still get forget from riot (except when they decide to nerf him).
After the guinsoos been nerfed, jax are so powerless when he facing the tank or fighter (e.g. ornn, sion, aatrox, riven and yorick).