Wrong rework
I like how riot fixes champs that don't need but then put aside 
because he isn't broken or anything
2 Comments
Let me put it this way, he was at a more updated state in his kit (subtract tweaks I suggest looking into it.) then say Kat (she's had the same kit for a LONG time same with Shaco.) But they gave it more room for 'counter' play. Xin has some counter play to his kit like the fact he's sorta slow and can easily get CCed like assassins can. :D
Warwick on the other hand needs a kit update, is a step down from Xin. He doesn't have a gap closer like Xin does unless you chase them down Autoattack them a ton, Q spam and then ult close. Generally Xin is luckily one of those that isn't super unbalanced nor balanced, but his kit isn't main priority and will probably get a rework after Irelia since Riot is trying to give skill shot based champions over point and clicks like they use to from those who had older kits.
xin is diver not assassin