[jltsiren]

A postdoc is a training position, where the individual further develops their skills and tries to build an independent profile while being mentored by a more senior academic. PhDs who work in someone else's projects without focusing as much on personal development typically have other job titles, such as project scientist or staff scientist.

Receiving a doctorate does not mean that you have finished your training. Some countries have habilitations or higher doctorates, which can be understood as more formal versions of postdoctoral training. Medical doctors are expected to specialize and receive more training as residents. Other fields have similar arrangements, some more and others less formal. If a full career is 50 years and the job requires a high degree of specialization, it can make sense to use the first ~15 years for training.

[timschmidt]

The number of academics who achieve a 50 year career is vanishingly small. I can think of a handful I met in a decade. To call the other 99.9% of academia in-training is a bit of a mis-nomer, whether it's the accepted terminology or not. That was my point.

[jltsiren]

And my point was that academics whose primary job is doing research in someone else's project are even rarer than tenured professors in research universities.

A postdoc is primarily a career advancement position rather than something where you are expected to contribute full time. Such positions are also pretty rare. There are something like 70k postdocs in the US, vs. almost 190k tenured or tenure-track full-time faculty in research universities.