IIN I hate when people say something is subjective like psychology?

I think the idea is more that someone with the same symptoms can see two different doctors and be diagnosed with two different disorders depending on how said doctors feel about the severity of the symptoms and the general level of self awareness of the patient.

A patient who is anxious, not very good around people, who has a hard time showing empathy and has a hard time looking past their little self box can be diagnosed as having social anxiety by one doctor (this person has a fear of people and by that virtue, has difficulty interacting with them due to their lack of experience stemming from their fear) and as having a personality disorder by another (this person is self centered, cold and doesn't like people so is naturally anxious around them).

It sounds ridiculous but it happens quite a bit with even seasoned Psychiatric professionals. A diagnosis doesn't just depend on symptoms but how the doctor sees the patient and how the patient presents themselves and their symptoms on any given occasion. Anyone with a brain can tell you that human behavior isn't always a constant.