I have played quite a few Xin Zhao games and I can tell you if there's one thing Xin CANT do is turn a game around. Of all (my) junglers he is most heavily influenced by a losing team; if the team loses their lanes early, Xin can get turned on rly easily and killed in his jungle.
I think what you're mostly seeing is because IF a Xin is ahead of you/fed he can be very oppressive and can indeed kill you very fast, for some reason people dont expect Xin to do alot of damage (maybe bc he's not as common as lee for example). Thing is** he is very vulnerable to burst and cc.**
He is very strong in the early game and can get him or his teammates fed, however if the enemy team gets back in it just a little or has the right types of champions they can easily shut him down. Once you're beefy enough to whitstand his combo (E + 3xQ) or have enough CC and burst to kill him before he can get his Q's off on you its over.
Ive had mixed results lately with AP + Sated Xin Zhao, its really fun and somewhat viable. You can snowball ur team early with base damages between lvl 2-5 (just like normal Xin), but with AP xin and a little feed and sated you're unkillable and ALOT of fun. However he struggles very hard in a losing team or vs burst + CC even more than regular Xin. The early game is fine, so is the later game once u get Sated + Nashor + Rabadon (u can tank turrets w/o minions), the mid game is a struggle tho if u dont secure some dragons for a fast Sated and have a losing mid lane.
In general Early game snowball champions are stronger in Lower ELO (mine, im gold V) because people tend to keep playing the same even if theyre behind or when they know theyre vulnerable to ganks
and ofcourse our