Not true in KTN. You can get off the plane in KTN even with the combi and go up the stairs to the secure area (though you need an employee to unlock the door). Other airports, you are correct. But the airports are so small that "passing through security" is almost a non-issue.
I didn't mention KTN because, as you mentioned, it's a terminal building with a small snack bar even. They even have jetways there. That said, if the flight's running late they won't let people off. As far as the security in other airports (except JNU, SIT or KTN), it can be a challenge on a full flight. Because some of the terminals don't have waiting areas past security they will only start clearing passengers as the boarding process begins. On a full flight from PSG (as they often are), it can take some time to clear security. Not the hour or so it can take sometimes in larger airports with maze like security lines but a wait none the less.