I think you are right about this.
When I started the "recovery phase" of my life, I felt depressed. I identified about 4 different kinds of depression that I either had then or had as a child. Meanwhile I was listening on FM radio to a radio-clinic-counseling-team. The psychiatrist on that team, Paul Meier, said that "depression was anger turned inward". But I knew I had depression which wasn't just anger.
So these are my thoughts about what is depression. I'm not disagreeing with you, just giving some old thoughts.
Depression was 4 things:
1. A feeling of sadness - emotional
2. A body feeling in which the body is somewhat stiff.
3. A slowing down of responses.
4. Anger turned inward