I agree that heroic effort can hide a resource allocation issue, but often the goals of those controlling resource allocation are not well aligned with the hero's goals. By no longer buying supplies for a student, a teacher is not going to get the school system to provide free supplies.
In terms of work in the job description, I could probably be replaced by 1.2 (1.1?) average competent workers. In terms of other benefits of my employment to coworkers and patrons, my impact is hard to estimate. Others bring in goodies for snacking, but I maintain a consistent but limited selection of snacks; others may spend as much or more money per year on snacks, but knowing that certain snacks will be available has significant value.
While I would have liked being promoted one level (from library page to library aide, from shelving only to shelving and check-in), higher positions have responsibilities I would have found extremely stressful. I was passed over twice for a promotion supported by my immediate supervisor (the decision was made by higher ups, the second time my supervisor was miffed that his input was not given more weight) and I had a meltdown at the interview for a third chance when technical issues (not working audio in an online interview) forced cancellation of the interview. I took my reaction as evidence that I was not ready for more responsibilities.
The first time I was not promoted, I was not especially bothered; the person getting the job was competent and went beyond minimal effort. The second time I was told that I would probably get the job (which I think was part of why my supervisor was not happy about my not even getting an interview) and the person getting the job seemed (after some observation) to be less competent and less enthusiatic than the previous transfer. (I think this estimate was not derived entirely from my disappointment: my first impression was "this is a library person" (glasses et al.). Perhaps seeing a library person not seeming enthusiastic about working at a library may have soured me more than if I had no hints of a kindred spirit.)
I like helping my coworkers (I like most of them and dislike none), but shelving books is not that team-oriented. I do not want to manage people (I am not good at it and do not enjoy it).