Why has jax got such a low win rate now?

His laning phase is very abusable. You can take him in the jungle to mitigate this, but his clear time is slow for a Devourer jungler, and his ganks, while pretty decent, are a huge mana drain, so if his gank fails he can be put behind.

Its more of Irelia is just flat out better right now.

He is still good, its just he is outclassed right now. If your good with Jax, more power to you, but in competetive try hard play, people are just flat out picking Irelia over him.

His early game is so weak that it often prevents him from reaching his godly late game. That's pretty much it.

Can't counterstrike the dunks or the demacian justice.