To answer those questions, first, we need to define the above-mentioned terms:
A mental disorder is a syndrome characterized by clinically
significant disturbance in an individual's cognition, emotion
regulation, or behavior that reflects a dysfunction in the
psychological, biological, or developmental processes underlying
mental functioning (American Psychiatric Association, 2013).
Mental illness is characterized as “maladaptive responses to
stressors from the internal or external environment, evidenced by
thoughts, feelings, and behaviors that are incongruent with the local
and cultural norms, and that interfere with the individual’s social,
occupational, and/or physical functioning (Townsend, 2015).
Furthermore, no books or reliable sources differently defined medical condition and medical disorder so, let's assume that these terms are synonymous.
By definition, medical disorder is any disturbance in a person's mental functioning that can affect his daily routine. Yes, there are medical conditions that are disruptive like patients with psychotic disorders, depressive disorders, substance-related disorders. The latter are considered disruptive in terms that they can harm themselves or others. They require therapies like psychotherapy, pharmacotherapy, etc.
Moreover, there are also medical conditions like personality disorders, human sexuality and gender dysphoria, somatic disorders, etc. that are less likely disruptive but can also affect the person's mental functioning. They can either function well in the society or unable to perform activities of daily living.
But still, all mental disorders need treatment whether disruptive or not. It is not about how harmful or peaceful the condition is; it is all about the person's mental capacity and functioning without any maladaptive adaptations
1. Townsend, M. (2015). Psychiatric mental health nursing: concepts of care in evidence-based practice (8th ed.). FA Davis Company: Philadelphia, PA.