Don't be so careless. China steals technology worldwide and already has a 5th generation aircraft. In this they are ahead of Russia. Where is the guarantee that the Chinese have not stolen enough information to create your submarine.
The problem with stolen technology is that you may not be able to steal information about the most important parts, and by the time you assemble your own sub using the stolen data, that technology might become obsolete.
The problem is that everything is always think so. Now the facts. Nuclear weapons in China has the missiles to deliver there, fighter 5th generation is, submarines are built, launched aircraft carrier and two more under construction. And it's not all the facts.