I’m not so sure that people who use those terms want to use them interchangeably.

"Rockstar" is a weird label for many reasons. Even though it’s ambiguous, it could arguably be used to qualitatively describe the person’s work ethic. E.g. They’re just more productive than any other professional in their role... They'll work weekends if needed to solve a problem, then crash for a couple of days... etc.

Full stack designer could be used to describe the competencies across the spectrum of design specializations. E.g. They can do both ethnographic research and design an high-fidelity interface mockup!

Neither of the above two needs to relate to seniority in any way. How many years someone has been in the industry doing a particular kind of work is a simple metric and not unique to the design field.

Good recruiters, who excel at their craft, should care about all these and be able to differentiate between them. I think it’s on us to coach them if they’re conflating things, or misusing the labels in a way that’s not good for the profession.