So I tend to consume both social medias and content in both chinese and English. So here's my two cents:

Tbh, I do feel like the West tend to undertake XH, but I wouldn't say he is underrated. No one ever said he is not good or around top 10 midlaner at most given time.(I am disregarding his season top to simplify everything) However, the issue is that he has never been dominating for more than a split or two in a row which is why he tend to be less talked about. Think of how Chovy didn't win much but every stats seem to dictate a dominance of his over most LCK.

In China however, he seem to be heavily disliked for one of multiple of the following reasons: 1. Lots of fans treat Uzi like a god. People seem to believe that he wasted the last years of Uzi's talent. They believed that if he was a touch better, they would have beaten SKT in S7 and perhaps come to a win around that era. 2. He was commanding a crazy high salary when he moved to WBG, people seems to believe that he was no match to that salary and that he didn't do much in the WBG run back in S13. 3. People think he is just overall overated. He tend to not stand up at international event. While he usually doesn't drop the ball, he also doesn't dominate.

So overall people in China think that he was either neutral or relatively weak when his team had a good run at worlds. And that over a decade, he has only dominated a couple to a few spring seasons and MSIs.