I can't help it if it is a long and arduous path to the career that they have chosen. But the fact is, they're still in the education system and learning/ gaining experience at this point, just like apprentices.

I don't disagree that the pay is shit and that it could go up a bit if it is actively discouraging people to do their PhD. Being used as cheap labour is a problem for both apprentices and PhD students alike, it seems.