That's the problem with people who think that knowing a subject makes it possible to get every answer correct. Some of the best courses I took had questions on exams that were not possible to answer correctly without access to a supercomputer and a few hundred CPU months, where the instructor was looking for depth of knowledge and technique rather than "the right answer". It makes me wonder if those that advocate for absolute grading have ever had to do anything difficult in their lives. Or ever considered that two exams on exactly the same material could have different difficulties.
It's also not true that scores are proportional to knowledge. An obvious example is the multiple choice, multiple answer test where negative scores are quite possible.
Typically I design upper division exams for an average of 50%. I could easily design for 84% "standard," but it would tell me and my students less, because there would be less distinction at the upper end. It would be more difficult for students to know what they do and don't understand well. Yet you would have me punish my students for making the people with As work a little harder and maybe learn a little more.
The problem is that grades are arbitrary. The instructor defines them, and the universities and the students pressure instructors to give higher grades in lower division courses. Instead of arbitrary grades, assign lower division grades by quintile. Top 20% A, Bottom 20% F. It's enough to maintain student competition, gets rid of the "easy graders". For higher division, drop the lowest grades, with F being giving to a small percentage at the option of the instructor. Mid division would be ABCD quartiles. Upper division ABC. Graduate AB.
If it's possible for a student to get a degree by taking only "easy" courses, that's a problem with the design of the major curriculum.
A right is not what someone gives you; it's what no one can take from you. -- Ramsey Clark