Base course loads vary between institutions. Some community colleges have course loads as high as 5/5, and teachers can have as many as 50 students a class. Some research institutions, like mine, have a 3/3, and I teach typically around 100 student a term, with no TA or grader. Some research institutions are 2/1, with grad courses with low enrollment and even TAs or graders. Some liberal arts colleges have a 2/2 load, which compares with some research institutions that supervise Ph. D and masters students, and have low class enrollment.
I also have no idea what counts as ‘teaching’ duties. Certainly class time, and well as prep and grading. But when a student comes by and wants to talk, even if it’s not about academic issues, I don’t shoo him/her away. That, I would assume, would be part of mentorship. And then, especially for first years, when you teach small classes, the students feel comfortable coming to talk to you, and then you get a whole host of issues that I never expected I would be dealing with: kids whose parents have thrown them out of the house, kids who are depressed, kids who want to change majors but don’t want to tell their parents, etc. etc.