I once had an author who railed at me for not finding an “appropriate” copyeditor for her manuscript. Her book explored how to interpret Latin American political history using game theory. She expressed dismay that her copyeditor was not an expert in these two fields, and moreover had no Portuguese and only rudimentary Spanish. I explained to her, as tactfully as possible, that a person with mastery of those four domains was not likely to choose freelance copyediting as a career.
Authors, the perfect editor is not necessarily one who shares all of your interests and enthusiasms. An editor who is a carbon copy of yourself is useful if you are interested in preaching only to the converted. If you hope to change minds about your subject, or to reach an audience unfamiliar with it, a generalist editor will be of greater service. The perfect editor is not the closest colleague in your field but a person who keeps in mind the concerns of the full breadth of your potential readership.