Xin is easier to handle then people think, stun him or break his attack combination and he will die really fast.
I play Xin so I have a pretty good idea what works against him
The biggest thing to remember is never ever try to out damage a xin that goes for attack speed and life steal, 70% of the time he will eat through the damage.
my normal setup when I gear is Melady, Phantom dancer, ninja boots, Stark, Executioner, and infinity edge
this gives me 115% attack speed plus 20% from runes and another % from aura
53% life steal
65% critical strike
15% movement +2 movement from boots
5% damage increase from tree
since I am not lvl 30 yet i haven't taken full advantage of bonus crit but with infinity, tree, and runes it is possible to get 75% more damage to the 200% bonus of a normal crit.
As you can see it is better to snare or stun xin then try to take him on, I have jumped into a group of 5 that wasted their counters on a tank and killed all 5 before any of them could get our of leap range.
I use the same build with Yi and it can be just as bad but without the slowing.