I can definitely attest to the argument that the material presented in pharmacy/med school isn't as hard to grasp as the more theoretical material presented in upper level undergraduate courses. I have a biochem degree and had to take some tough chemistry courses, like physical chemistry/quantitative analysis and of course those upper level, more in-depth biochemistry courses, advanced immunology, etc. Theoretically, they were harder to grasp then pharmacology/pharmacokinetics. In fairness however, my background in those areas probably made it easier for me to grasp those concepts in pharmacy school.
I finished undergrad with a 3.85 gpa; I'm a pretty damn hard worker and honestly it didn't kill me. Comparably, P1 year wasn't bad at all. It was similar to undergrad, with perhaps more courseload. P2 year was like a bat of hell. The pharmacology/kinetics, med chem, and onslaught of therapeutics (Wayne State's curriculum is very therapeutics heavy) just came so fast and got so in-depth. If the subject matter was as difficult to understand theoretically as undergraduate level courses, then it would be impossible to make it through the curriculum. In retrospect, my undergrad was about a 5/10 in terms of difficult and pharmacy school was 9/10.
I think curriculum wise pharmacy school may just be slightly easier then med and dental school in terms of didactic training. In terms of clinical rotations, there is no comparison. Med school's rotations are harder, longer, and require more hours, plus the USMLE steps, etc. However, depending on the rotations you do in pharmacy school, you can get a very challenging (and rewarding environment). Rotations IMHO are what make a great pharmacist. I for one did almost all of my rotations in various ICU environments at a trauma center and I had a killer HIV/Amb care rotation. Spent about 60 hours/week at my site. Still not as tough as med school, but tough.
I can't comment on law school because its so different. I think what makes law school hard is the competition between students (this is also somewhat true for med school). Pharmacy school really doesn't have much competition beyond those striving for residencies. Also, in law school you got one big exam at the end that can make or break you. In comparison, pharmacy school is a continuous onslaught of exams that constantly keep you on edge with that pit of fear in your stomach. It's a totally different learning environment and I think both are similar in terms of difficulty.