You don't want Jax to be buffed more
I am seriously in fear everytime that Riot buffs him, that he will return to be what he used to be. I felt that when they buffed his ult recently.
What I want to say is that, there is a reason why 
has the same level 18 health as Kog'Maw. There is a reason why his base armor has been nerfed to be one of the lowest in the game.
The reason, you ask? Before those nerfs, Jax used to be a monster. A monster that was impossible to 1x1. There wasn't a single champion in the game that could outduel Jax; I imagine that the only exception would be peharps a well-farmed late game Nasus, with Thornmail. I've never seen that matchup on pratice, though, so I can't say who would win.
Even when purchasing only offensive items during the early game (Trinity Force and Blade of the Ruined King) he could still be potentially as tanky as a champion who actually purchased tank items. And then he could build actual tank items, and become a monster that not only was extremely tanky, but also had a lot of damage to boast.
Jax was a very dangerous champion. You think that Riven is obnoxious as she is now? Then you don't remember how Jax were before, he was a lot worse. Even when using a champion that could be called a counter to Jax (ex: Renekton, Malphite, Vladimir) you would have to be extremely careful and know what you were doing, as a single mistake meant that Jax (at least a good one) would all-in you, kill you, and win the lane regardless. And with that, counters didn't meant much.
Remember that Jax, at time, used to be as banned as Kassadin was from draft games during the time that he had a silence.
Riot tried to adress those problems with the health and armor nerfs. Now Jax:
- Actually has a weak early game
- Actually has to purchase tank items early if he wants to be tanky
- Many champions can now have a chance to out-trade or duel him
If Jax is balanced nowadays it is all because of those nerfs, so you should be thankful that Jax has the same level 18 health as Kog'Maw.
