The key differentiator is that in China your smartphone can in many ways be abstracted down to the platform that runs WeChat. So Apple's key lock-ins like iMessage and FaceTime don't matter and it has to compete on price.
Apple greatly increased prices in the US/EU also and many of these regions are facing a recession too, but according to Tim Cook's letter those consumers didn't abandon the iPhone. What's unique to the Chinese market? WeChat.
Hmm... I'm not convinced by that. At least in the UK, I don't know many people who use FaceTime (WhatsApp and Facebook Messenger are the most popular video chat software). People do use iMessage, but that falls back to SMS if you don't have an iphone, and SMS messages are universally free here these days.
But in UK, there is not too many alternative phones, like Huawei, OPPO/vivo, Xiaomi. All those local players in China are based on Android, but still provide customized OS with unique features.
As a UK counterpoint, most of my friends and family (at least 15 people) use iPhones and iMessage/FaceTime is a major reason for sticking to the Apple ecosystem for us.
