Those are typically skills a starting scientist needs to learn. At the same time, sometimes it does feel abusive especially if the student doesn't get some sort of credit for doing the peer review and talk prep.

In my program the main reasons people took a long time to graduate was: by year 6 you are usually very well-trained and highly productive (making you very useful to your advisor), and advisors often require you to publish an important paper in a major journal (Science, Nature, Cell) before they sign your dissertation.