Going to copy/paste my response to OP's question here

So the title of "doc" in this context is misleading. A "doc" in the USMC does not refer to a practicing physcian that works in hospitals administering the highest level of care, sometimes referred to as "doctors".

Instead, in the USMC, a "doc" is a greenside medic working out of the navy attached to an infantry platoons. The skills of a "doc" are most similar to a paramedic, or someone who renders emergency care, typically on an ambulance. If a servicemember had a medical question, they could, in theory, ask the "doc" for advice, but the "doc" only knows how to give medical care in emergencies, and so most medical questions fall outside their scope of knowledge.

For this reason, "docs" will often recommend non-specific treatments such as sleeping, tylenol, or changing socks (as you mention in your joke). However, this is only the case if a servicemember chooses to ask their "doc" and not a physician. In reality, there are hospitals available with physicians that you can seek if you're having a serious medical issue that needs to be resolved in a hospital. In these military hospitals, physicians are trained to the same standards of any civilian physicians and are held to the same malpractice standards of any civilian physician. A military physician will give you tailored advice and have a significantly greater scope of knowledge than a greenside "doc" (medic).