I work in the mathematical sciences; specifically, I am a theoretical physicist (with a Ph.D. in applied math). And I can state that, in many cases, an student's advisor may do as much work as a student on a calculation, even if the student seems to have performed the whole calculation themself.
This may seem like a puzzling contradiction, but there is really a simple explanation. A student's advisor may be doing quite a bit of work that doesn't get noticed. When I give a student (particularly an undergraduate or even a relatively junior graduate student) a calculation to work on, I may need to do the whole calculation myself, at the same time the student is working on it. That way, when the student comes to show me their work, I can spot any errors and give them guidance how to get through the difficult parts. Sometimes the students may not even realize that I have done the calculations independently myself.
As students get more mature, and my confidence in their abilities grows, I don't feel that I need to do this as much. When I'm working with more advanced graduate students, I'm generally happy just to check over the calculations that they do first. However, it is still commonplace for me to find errors or points of confusion in the students' work.
Obviously, I also provide a guidance to students about what problems they should be tackling and how their results should be interpreted. Then the question becomes whether all these contributions are sufficient to make me an author on a student's paper. I generally leave this up to the student. I'm a tenured professor, and I publish enough that I don't need to worry about counting publications. However, even before I had tenure, I left the decision about whether my contributions were sufficient to merit authorship up to the students. We discuss the matter and how much each of us has contributed to a project, and in every case, the students have decided that I should be included as an author.
Other faculty may be less relaxed about this question and insist on being authors on their students' papers; and in many cases, I think this is fully justified. As I pointed out above, an advisor may need to do all the same calculations as a student (and possibly more carefully). Moreover, I don't think it detracts from other people's impressions of a student's work to see their advisor as a coauthor. If I see a paper by a student, I often presume that their advisor played a crucial role in devising, checking, and interpreting the results, unless I have a specific reason to believe otherwise. However, I do not view this as any kind of negative reflection on a student. Even the best students need guidance; that's why they are students.
Of course, there can be cases where an supervisor declines to be included on a student's paper. This happened to me once with my Ph.D. advisor. He had been working on a problem with another faculty colleague, and they asked me to look into it further. In the end, the published calculations were done primarily by me and other professor. My advisor contribute one small result, which, so far as I know, had never previously been published, but he felt that it was too obvious to earn him a place as an author. So the authors on that paper were me and my advisor's faculty colleague.
Ultimately, different faculty members may have somewhat different feelings about authorship in these situations. However, it is easy for students to underestimate the amount of work that their advisor has put into a project. And including the advisor as an author is not likely to change readers' evaluations of a student's work very much. So my advice is that you are probably worrying about this too much.