That's not a good example of scrubs QQing. 3 months ago, Jarvan was pre-nerf, Irelia still had everything but her ms (which admittedly hit her pretty hard), Xin Zhao's ult still made him impossible to kill, etc etc. Literally every usable tanky DPS was better than Jax l0l. And Jax used to be alright just because ranged AD used to take solo lanes. Now, his only viable position is top, where he loses lane to a lot of stronger laners unless played by hotshotnidaleegg.
Anyone smashing today?
Yes, Jax was picked because everyone else was nerfed due to a mixture of QQ and tournament results. The whole point of nerfs is to bring down the power levels to make other heroes viable choices. Of course the community's reaction after seeing Jax at IEM Cologne was to whine for a nerf; Riot listened. Why should people experiment and come up with something that counters X champion, when they can cry on the forums for two weeks and get a nerf?
Also, Xin's ult definitely didn't make him unkillable. If he was, he's built straight tank and did no damage. He's a 100% auto-attack hero: Q provides knock up CC on the
third hit. W is an attack speed steroid that reduces his other cooldowns everytime he attacked. E is a gap closer with a slow. and R is an AOE attack dealing base damage + 15% of enemy's current health in physical damage and providing armor and magic resist depending on how many heroes you hit. If you CC him while he has his Q or W up, you mitigate a lot of his damage and he melts if you build straight damage.
The problem with having melee carries is they can't achieve hard carry status in this game save for a few. Building damage sacrifices defenses and vice versa.
Edit: I would also like to play some smash today lol