Exactly. People are missing the point that bringing in new customers is a lot harder if you have to go through a number of additional loops to install an app and even find out about it. Local rivals have a massive leg up. Over time, once local rivals develop and they are easily accessible and feature rich, then people will stop using the Chinese apps. Just look at the latest YC batch which was full of Indian startups.
Facebook Messenger also "wasn't even started till 2011". Before 2011 China had very mature local messaging (QQ, from the company behind WeChat) and less mature but burgeoning social networking (loads of them I believe, including part of QQ). Cherry-picking the date of one next-gen product that later took over is meaningless.
Hmm...per Wikipedia the original Facebook chat was started in 2008. Facebook Messenger for mobile was 2011. QQ didn't have their mobile version till 2013.
Facebook cannibalized social networks in the US and homegrown networks abroad. Though we'd never know, I'd believe they would have done the same in China.
Facebook was blocked by China in 2009. WeChat wasn't even started till 2011.