I have to agree here. I am going back to get a 2nd BS, this time in a technical field, and I just finished discrete mathematics (at a community college no less). We used Rosen, 8th edition, and I had single homework assignments with enough problems to fill up 6-8 hours if you include the readings required. It was probably one of the most challenging classes I've ever taken.
One thing that stood out for me as well was that someone else indicated that, in general, the only requirements were the exams. Most of the engineering classes I took had weekly problem sets that, yes, took at least a solid evening to do.
The way my undergraduate did credits was the (theoretical) number of hours a week they took between lectures, lab, recitation, and study/problem sets. Typical classes added up to 12 with usually 4 hours of the first 2 categories and 8 hours of the last. Classes varied but that wasn't too far off for the typical class. (Though there were some real time sink outliers.)
I actually read that as 2-3x the in class time. No, where I went people generally spent way more than 2-3 hours/week of their own time on many courses.
And then the proofs. Oh the proofs.