would the threat of "We can get you anywhere" have discouraged defectors?
The KGB did in fact
assassinate defectors. Total effects from this policy, other than generating anti-Soviet sentiment in NATO countries, was quite limited. People willing to defect, with high risks plus all of the ordinary consequences such as cutting off all contact with family/friends on the other side of the iron curtain, tended not to be easily deterred.
NATO countries, including the US, went to significant lengths to protect defectors, especially those who had brought valuable information. New identities were created and security provided, much like the Witness Protection Program. Such tactics would likely be effective against Soviet efforts short of assassination as well.
The critical element that makes current Chinese efforts potentially effective is the Chinese government's efforts to permit Chinese university students to study abroad. They represent the primary population targeted, are extremely vulnerable to threats, and provide enough value to justify the expense. Nothing comparable occurred during the Cold War.