Lack of credentials doesn't mean lack of knowledge, but their presence is at least
some signal. Your story is a stronger signal, that's why I asked about credentials
or personal experience.
What you wrote above puts what you say in perspective; because it adds qualifications to the statements that you make (i.e. that yes, you are not taking things out of thin air). Without your story, it's not possible to evaluate where you're coming from, and how to take what you say.
Thank you for sharing your story, and sorry that the journey has not been easy. I'm glad and thankful that you made it through to this day.
That said, I respectfully and strongly disagree with your assessment "this os why depressed people suffer". Perhaps it's cultural, but I'm from Eastern Europe, and happiness was never supposed to be the default; the culture is rooted in misery and suffering.
The cult of happiness seems to be a Western thing, resulting in a culture of toxic positivity which is definitely not conducive to mental health. The Eastern culture of never-happiness isn't healthy either, but "the truth that depression reveals" is just the narrative of that culture — and it's just as false, and, furthermore, easily accepted.
The entirety of the Russian-speaking population of former USSR starts off on the assumption that things suck and will suck forever, and do not conclude that there's nothing to live for because of that. That can't be the why.
When I was at a conference in Belgium, a Polish person in the group asked me when we were coming back from a day trip to Liege: "Why are you smiling?". See, unless there's a good reason, a an outward expression of positive emotions sticks out as odd. Things are supposed to be grim.
And yet neither it is depression, nor a cause of suffering.
I'm also Jewish, and again, suffering and persecution is a part for the culture. My birth certificate says "Jew" (yay USSR keeping tabs on who's who!), so I have a very formal reminder of being a target for those who still look for them (as Pittsburgh has shown). My father's father went through the War being a target in much more direct way.
So there was no "truth" that depression has revealed to me. If the horrendous life experiences you went through have helped you get rid of the rose-tinted glasses, well, it's not the worst side-effect. If losing them was painful, you can thank the culture for that (go figure: telling children early on that they can do anything and always succeed and be happy if they try hard enough creates some highly unreasonable expectations both internally and externally).
That pain is not why people with depression suffer. That pain is why people affected by the cult of toxic positivity (aka "live, laugh, love") suffer. It just adds extra work and pain on top of dealing with depression.
And yet, going through these realizations is neither the cause of depression, nor the fundamental reason of suffering.
Because through all the pain and suffering, a healthy mind still sees finds something to live for, and a depressed mind does not.
And while it's natural to not be sure what it is, the dead-sure confidence that there is nothing worth living for that depression gives is not "truth" in any way.
If only because that's making a call about the future (i.e. that nothing going forward would be worthwhile in retrospect), but nobody can tell future for certain.
Externalizing depression as an entity that's not speaking truthfully is a way to start pulling yourself out of it.
You have enough resources to evaluate the above by reaching back into what you learned in psychology classes. My experience with depression has been personal — by being depressed for years, and then being in and out of depression. My understanding has been corroborated by experiences of my friends, people who talk about depression online, popular psychology, experience with therapists and coaches, and numerous bloggers and book authors who write about depression (Allie Brosh, if I had to name just one).
And the consensus is universal: depression lies.
PS: depression tells me that everyone hates me and that I'm worthless when I forget to eat and sleep, and suddenly it seems to not be the case after I eat and sleep. Any "truth" about the external world that depends on how full my stomach is, well, isn't truth at all, and it would be foolish to accept it as such.