Look I don't know if you're trolling or not. But... As I said, it's well known that there have been significant and painful breaches in security by Chinese spying efforts. You can keep talking about cybersecurity and whatnot, but no defense is infallible. And it doesn't matter if your computer is connected to the internet or not. The game we're talking about is intelligence, and both China and the US spend ungodly amounts of money on both intelligence and counter intelligence operations.
Cyber operations are but one part of this game, and honestly it's not even that significant for intelligence. Cyber security is more about keeping your networks safe and working because so many parts of our society are now dependent on these networks (i.e. the electrical grid, or traffic controls). Any self respecting data manager would never keep real sensitive information on a networked machine, what you're talking about has been standard procedure for as long as networks have existed.
You don't steal information by "hacking" that's for TV shows to spur the imagination of people who never think about intelligence operations. In real life you steal information by performing intelligence operations
like the famous honey trap operation performed by the Chinese spy "Fang Fang". You let people infiltrate organizations, or you bribe or manipulate a target into providing you with information. HUMINT is still the core of intelligence work, and China is very good at it. For example, there are sizable Chinese diaspora all over the world. And many of these people can be pressured, or persuaded to provide intelligence.
So to think that China wouldn't be able to steal secrets because there's cybersecurity and protocols, just means you don't understand how spies go about stealing secrets.