I have been assigned 6 teaching assistants to cover 16 seminar groups. But despite the 6 people to help me out, all the troublesome aspects of university teaching such as dealing with plagiarism, student complaints about marking, students who require special accommodations due to illness and that sort of thing falls on the professor and not on the TAs. Managing the TAs and other administrative aspects take up quite a lot of time too.
But some colleagues have only 10% of my course enrollments. In some cases this is due to their reputation as ill-prepared and uninspiring lecturers so students stay away from their courses in droves.
But actually the lousy lecturer has a lot less to do because their lousy courses attract fewer students and and require few if any TAs. So the lazy lecturer can put more time into writing articles for publication. That is why it is called "teaching load" and "research opportunities."
My conclusion: To succeed as an academic, teach badly.