The reverse double diamond is a far more common situation in reality. Andy Budd provides insight into why it is more common, and why it makes more sense for the business.
Designers tend to want to work from a clean slate—a problem—but more often the business already has insights and ideas as to what the problem is, and how it should be solved. Additionally the business often has far more knowledge of the problem space than designers, making them more qualified to suggest a solution.
Obviously this all varies from org to org, its size, and area of expertise, but I personally think that designers are responsible to determine how product-savvy—and design savvy— the business people are, and suggest the proper way forward from there.
If anything, the reverse double diamond defined as such is a relief almost, as in just realizing that we are not the only ones stuck with not being able to do things the “proper way”, when the proper way is actually more of a theory, and is rare in practice.