Over the course of years a story has been pieced together to tell people. Atoms weighing a certain amount fuse together. When they do so they weigh a tiny bit less, with the missing mass being converted to energy. That explains fusion, and the way the sun works. (Yes, I deliberately used both weight and mass. Hey, so did you.)
This is simplified, but is extremely useful as a way of understanding a complex process. You can tell people to give it up, but if you do you have to substitute another story in its place that yields understanding.
Stories have rules, just as much as physics does. You can’t introduce terms at will. A few terms have been around for a long time and will be accepted. Every other one has to be explained. Explanations take space, of which there is always too little.
Mass defect is a term that is not used in popular science. Potential energy is barely within the rules, and probably needs flagging. You don’t get to say that these rules are wrong.
If people do hear “mass defect” they will naturally ask where the mass went. If its all energy to start, some of it in the form of mass, and all energy at the end, some of it in the form of mass, then you’re saying that mass is convertible to energy whether you intend to or not. Even talking about conservation of mass isn’t sufficient, since the story of relativity includes a tale about having to give up the separate rules of conservation of mass and conservation of energy and substituting conservation of mass-energy.
It took many years to get from the story of electrons orbiting the nucleus like planets to a story of electrons forming a probability cloud with no definite position. That may be equally technically wrong, but it’s a quantum story that people will accept, and it shows that stories can change over time.
What’s the new story?