A doctor has experience/knowledge in treating diseases.
So you are arguing that only a doctor with cancer should treat cancer? Otherwise, they have exactly zero "experience" with that disease. However, they do have knowledge through study and that is very much applicable. And, regarding moral truths, clerics are in the same exact position. After all, for all you know your doctor who has just advised you to get more exercise and eat less fat is immediately going home to veg on the couch and eat gallons of ice cream.
Additionally, while they likely have little to no experience of sexual relationships (this varies as I know priests who are widowers), they do have experience of chastity which is very much relevant to people of all vocations. They also know what it is to sacrifice for love in a relationship, which is what they do everyday. For somebody seeking advice on living a moral Christian life within their marriage there is likely no more relevant or helpful place to turn than one who has both a knowledge base resulting from study, as does a doctor in terms of medicine, as well as a working knowledge of conforming their physical desires to the will of Christ and living chaste lives as clerics do.
No I’m not. If I were, I would have said ...treating cancer, not diseases.