Did you even playtest Xin before you buffed him?
You literally can't even deal with him. He has so much sustain and damage that if he gets on an ADC, they're dead in two hits. He can melt tanks. He can get CC'd and instantly heal it all back up with his insane attack speed and buffed healing ratio. Watch his win ratio jump from 50%- 60-70%. Because he is insane right now.
You guys keep leaving powerhouses up while neglecting other champions. You buff already strong champions and let others fail. Mundo was ridiculously OP, with a high win rate, and banned instantly every game for around 3 months. Patch after patch, he still ran rampant. Same with Graves recently. Mundo is still a strong pick. But hey, lets nerf some OP champs and introduce a new item that warrants a wider variety of bans (while still keeping a 3 ban per team limit) and let's buff champions like Xin Zhao and Fiora because, ya know, they just weren't at the one-shot a squishy point yet. Oh and Fizz. Better buff him, too. He can one shot squishes, but why not buff him to make it to where he can AoE one shot an entire team? Your balance team is mint.