As an update to this: They DO care about companion benefits. They used to not care, but in April I had to put up a big stink with the Jeju manager because magically they decided to care about the other bags in my group. In July I went back to Jeju and on the way home, the only other person checking a bag besides me - she did not tag his bag as priority, but she was actually nice so I didn't put up a fight haha (the agent in April was not as nice). And yes, I did this in Korean and they said "family only is allowed if they're not morning calm."

That being said, we have BOARDED NO PROBLEM. They don't actually care as long as the Morning Calm person goes first (me but my bf is not morning calm aka Skyteam elite)