Given that most US websites are now over HTTPS, breaking PPTP won't actually give Chinese government much information to eavesdrop on. They may know that someone is accessing Google or Twitter, but they cannot know the actual keywords or tweets they are reading.

Note that Chinese government does not have backdoor access to those US websites, nor do they control a significant fraction of Internet infrastructure.

What about Chinese signed root certs?

That is why it is recommended to untrust every Chinese CA from your system. It won't affect daily browsing even for most Chinese users. The super majority of Chinese websites, even state owned ones, buy certificates from US companies.

Yes you can. Shadowsocks was intended for the similar purpose of tunnelling traffic and it is a bit more flexible than GRE-based VPNs