On one hand all these PhD thingies are very very important, and on the other hand words like "assets" and "commodities" are used for these same PhD people.
Author here---I mean the term 'asset' in a positive way, but I am also not a native English speaker, so maybe something gets lost in translation. Sorry about that!
My favorite term they use in academia is "trainee" to justify low salaries. Trainees encompass High School Students, Undergraduates, to Postdocs, an age range from maybe 18 to 38.
To be clear, students are paid stipends, not salaries. Stipends are low because they are stipends.
Depends on the system. In EU, these are often salaried positions as well.
Author here. Yeah, I am also still a trainee or an 'early career research' or a 'junior researcher.' These terms are...weird.