That's not quite right, although yes WeChat rules in China. Having the new shiny does matter - source, my wife is Chinese and I have a Chinese sister-in-law and niece both which got the X last year.
They are absolutely typical Chinese consumers in this regard. As soon as iPhone because hard to distinguish from other phones they switched away. As soon as iPhones became clearly distinguishable again they switched back. This is not just an observation, they say this is why they did it.
I think there are actually three factors hitting Apple in China this year. One is that a disproportionate number of purchasers got the X when it came out because it was so distinctive bringing forward purchases from this year, then there are a lot of Android phones now that look like the X models and the new X models don't look enough different from the original X to look new, finally the economy in China is pretty soft right now and people there are worried about the future.
You missed the fourth, which is a trade war going on that is inducing a soft boycott of iPhones. Some of those users may be lost permanently to local alternatives.
What phone you've got matters little as a result. So Apple doesn't enjoy its usual iOS-stickiness factor.