I am astounded, and humbled, when I see the long, long list of books written by some authors. Diana Palmer and Nigel Tranter come to mind, although they are by no means the only authors with a huge body of work already published.
Other well-established authors have published one book every few years rather than several per year. Is the work better if it was years in the writing? Perhaps, perhaps not. Diana Gabaldon is one whose books come out every few years, and they are spectacularly good. Nigel Tranter also writes well, but he has produced a substantial number of books. Some authors may simply have a different style of working, or outside commitments such as family, that slow their personal writing productivity. A few of whom I have read have the luxury of assistant writers and researchers to speed the process.
Having started late in life, and having little outside assistance, I have no illusion that I will ever manage to write, much less publish, more than a relatively few books. Nonetheless, I will write what I am inspired and able to write, and that is enough for me.
Have you collected or read a large number of books from one author?