The reason we don't sell bleeding edge technology is that no one wants to buy it. Why buy 1 jet when you can buy a dozen from last generation? 1 jet doesn't have superiority over 12.
Two points:
People do want our bleeding edge equipment. Japan has wanted F-22s for years. We won't sell them.
The level of China--Taiwan mutual espionage is incredibly deep. Every once in a while you hear about Taiwanese military officials has high ranking as general being arrested for espionage. While Taiwan is nominally our ally, you have to run under the assumption that China will quickly know about anything we give them and anything we tell them.