A typical setup would be to have a professor give 3 lectures a week, along with open office hours, and design the curriculum. Then to have an assistant or two who are graduate students (people who have a bachelor's degree or master's degree in the subject) who help grade homework, set up lab work, and answer student questions in a 1-hour recitation/discussion meeting.
It is virtually impossible to get into a teaching position post-doctorate in the US if you have not been teaching as a doctoral candidate. I have taught in Unis where there was an entire team of doctoral candidates (and a couple master's candidates) teaching a big chunk of the classes offered to undergrads - not as assistants, just as the listed "professor".
I have also followed open courses online where the "Prof" gives two or three classes in the semester, and the "assistant" teaches the rest.
As far as I know and have experienced, what you are describing is less true every year.