What you say is true, but Russia can easily become an enemy of China.
Not as easy as you think. Russia needs money and China needs resource and has a lot of labor. China's strategy definitely is to transfer as much Russian technology as possible when Russia either has to abandon it or sell while it still can. Meanwhile American weapon makers are just hyping things up for whatever reason.
Because no body really lost anything due to hacking. Do you really believe anything valuable (for the government and military) is even accessible from the internet? They have internal networks separated from the internet.
The reason the US is accusing China of hacking is simple a way to deepen the impression that the Chinese are pirates of intellectual properties. The US is probably using this as a bargaining chip. China of course has complained about a lot things on the US side but the US media will not report them or report them in way that makes China seem unreasonable.