Exactly. one tool you learn is how your thoughts/feelings/actions interact:
You cannot control your feelings, but they do influence your thoughts. You can control your actions, but they can influence at least some of your feelings. You can control some of your thoughts, which will influence your feelings.
(I may not have stated this exactly correctly, but the gist is the same ). So basically you learn that if you begin "investing" in healthier actions and thoughts (i.e. not sulking or self-pity or rumination), it will slowly pay off in less negative feelings.
No it doesnt' solve every single problem in your life, but a big part of depression is "learned helplessness" [1], and learning about thoughts/feelings/actions can be the first tool to counter this.
Still, if you did have that set of tools going in, but for whatever biological reason it didn't matter, then I would guess that CBT would be dust in the wind for you.
Medication was the life preserver for me when I finally got myself to accept that I would never be able to deal with this alone. Medication gave my brain some well deserved rest, let me take stock from a more balanced point of view.
CBT was my ladder to climb out of hell. Without CBT I would be still where I was those years ago, just less affected by it. Sitting in a room that was on fire, but just not caring about it that much, that's still a shitty place to be in.
The important thing about CBT was for me that it gave me tools to work with. A chisel for my mind so to speak. It is not at all about talking oneself into happiness, for me it was about NOT talking oneself into sadness. About giving me the logical framework to force myself to see good things where they were, instead of focusing on the bad things. It gave me ways to correctly differentiate between tackling bad situations and just glooming about non-issues.
I'm pretty sure without CBT my life would be nowhere where it is right now, so i'm very glad for its existance and would recommend anyone in a similar situation to try it with a GOOD therapist (mine was a guardian angel, battling the worst parts of my reasoning when I wasn't strong enough to do so).