Ask them all to take a month off and see which has greater impact and over which timescales.
Usefulness and value have different dimensions that can be orthogonal or even in opposition to one another. Many of us have worked in the presence of brilliant assholes and had to ponder that question.
There are lots of problems with the way universities are set up, but, from the point of view of a faculty member and, I suspect, also that of a student, "more leadership oversight" would solve none of them. (Unless it was accompanied by a change of university leadership from those who think of a university primarily as a business, to those who think of a university primarily as a university. I have only spent a long time at one university, so it is possible that this problem is peculiar to my university, but my impression from talking to my colleagues is that it is not.)
While faculty basically no matter how useless can never be fired.
"can't be replaced" has two opposing meanings in your post.
This describes the situation of tenured faculty (who are definitely who I had in mind when I referred to splashy big names), but universities have long been moving to a model with as few tenured or tenurable faculty as possible, where some instructors are full time but non-tenure-track, and others are part time (and so, for example, don't have to be paid benefits). At my university these are called lecturers and adjuncts, but other names exist. Both jobs involve renewable contracts (of different lengths), so they need not even be fired, just not have their contracts renewed.