In 1979, Vietnam possessed a battle trained army full of veterans of the wars against the US and France. Further, they were on the defense. Here, the Chinese will be on the defensive.
Cross half a continent to invade a country with a 3 to 1 population advantage with military tactics that emphasize armored breakthroughs and maneuver. Is this the Soviet invasion of China or Barbarossa?
Most of the troops that fought the Chinese were conscripts. The veterans were fighting in Cambodia.