Part of the difficulty with emotional views of problem sets and tests at universities is not so much that these sorts of problem sets are emotionally trying themselves, but that from the student perspective, going between institutions and class levels, the style, grading and expectations for problem sets and tests can change quite quickly. While I strongly prefer the sorts of problem sets being described, and preferred them as a student once I got used to them, it is likely helpful to have these sorts of explicit clarifications, even in situations where you might assume that students will already be acclimated to a particular style. For students taking unusual pathways through courses, they may not have been around for previous mentions in prior classes, may be taking a class out of their field or usual level, or may be more used to a institution, field, department, or simply instructors, with different expectations.
Going from secondary school or community college to lower division undergraduate classes, upper division undergraduate classes, and graduate classes, depending on circumstances and field, you can, in a few years, go from assignments where you have 60 questions you are expected to be able to answer, and getting 50 right will result in a poor grade or even failing, to assignments where answering 3 out of 5 is considered great. Without context, it can be terrifying to get a problem set where you assume that having trouble with a problem means you don't understand the material well, when in reality it's expected that you won't finish it perfectly even as an excellent student.
In my undergraduate experience, going from a community college, to upper division undergraduate physics courses, to graduate physics courses taken in my senior year, I went, from the finals one term to the midterms of the next, from classes where I walked into tests expecting that I should be able to answer every question perfectly, to classes where my 70% score on the midterm (of a handful of questions) was considered an excellent result, with no explicit indication beforehand that this would be the case. That switch was only a year before I was in a small graduate class where answering two out of four questions correctly on an assignment merited a congratulatory email from the professor. Even rationally having a sense that the expectations and styles were changing, it can be a massive, rapid shift.