The 1 thing xin needs to be in competitive/high elo

First off, it's really hard to enjoy playing champions that feel one dimensional. When I say xin is one dimensional, I mean that you can pretty easily anticipate everything that he's going to do. That not only makes the champion fun to play, but it means you can't really make individual plays that win the game.

I think xin's overall kit is good. I could go into a long discussion on why I think it's good, but rather than type an essay, I'd like to comment on the one thing that I think he needs in the way of changes. He needs playmaking that doesn't overload his damage. He needs a gap close that isn't champion targeted. My idea is virtually the same ability, except not champion targeted. This would allow him to make plays with his ultimate, almost like another lee sin, and it would enable him to jump away if he gets caught or gets low in the middle of a fight. "Xin Zhao leaps to a target location and slams the ground with his spear, dealing physical damage to enemies in a small aoe while slowing them."

If so desired, you could add a small thing or 2 to it. Like a slightly extended slow radius, or bonus damage to minions and monsters. But I think the key to making xin competitively viable is making his E non champion targeted. Make it ground targeted, but don't make it like vi where it has to pass through things. Everything else in his kit is good imo.