I don’t think anyone is suggesting that self-esteem building is the end all be all of solutions to life’s problems. Again, as a psychology student you should understand this from Maslow’s Hierarchy of Needs. Namely, if a person is hungry, sure, self-affirmation is not going to meet that basic need. If a person is lacking social affirmation, it is unlikely they are going to be able to meet their need for actualization through ONLY self affirmation (although MORE likely than being able to feed themselves through self-esteem

)
What is being said, however, and what is quite different than the straw man you are setting up to knock down, is that self-affirmation is an important need to be met in the process of self-actualization. Even Rascalking carries out self-affirmation, though he’ll probably never admit it.
Sometimes depressed people show physiological symptoms. SOMETIMES. Other times they don’t. A good friend of mine commited suicide after relapsing into depression. He had gotten treatment and his psychologist (a doctor of psychology, mind you) THOUGHT he was progressing nicely. Everyone… his family, friends, girlfriend, thought he was doing fine. Why? Because he was smart enough to control his physiology and therefore not to exibit any external signs of depression. In the meantime he had bought a gun and we know how the story ends.
You can’t treat the psychology of depression merely in terms of external symptoms. PTSD for soldiers, as an example, often manifests in internal ways without showing externally for some time afterwards.