I don't really like All-In Xin in dominion. he is very much a 1 trick pony. He charges, knocksup and deals significant burst.
However, if the enemy is able to escape melee range they can easily kite Xin since his charge is on a 12 second cooldown. Xin also has no Plan B. He can't decoy, cant toss stuff at range, no self shield, no nothing. He is do or die.
Xin has been heavily nerfed for Low ELO players who get stomped by his killer offense. Hence his offense is still strong but not as strong as it was. This would be fine, except that Xin has no finesse or utility or other tricks, unlike most other champs. His scaling is subpar too.
Therefore, he winds up being underpowered, as you can see by comparing him to similar champs. His skills scale on AP of all things, deal magical damage, and he only has an Attack Speed steroid to boost his autoattack.
Compare to WuKong with his Decoy, his AD-scaling skills, armor-breaking Q.
Or Lee with his heavy AD-scaling on his skills, along with self shield, blinks, anti-stealth, and other cool stuff.
Or Noct with heavy AD-scaling skills, AS steroid, AD steroids, shield defense, movespeed booster, and pretty good CC.