I've had MDD for about 17 years now and I tend to avoid these topics.
Technically you might be right, "never tell someone with depression to just, cheer up" or trying to give insight into how shitty it can be. It ends up being a thread of justification to accept their current situation because it makes it seem like its outwith their control to set things right.
It's ok to justify your circumstances, to a certain degree, to be made to feel like a your inner core youre still just a normal person like everyone else, it gives us support and makes us feel a little better. But that support is also a crutch, because good things/feelings whatever rarely seem to come and go and when it does we can latch onto it for too long, which in turns blinds us.
We still have a lot to learn about the mechanisms of depression and how it affects us, its cause is usually stated as an imbalance of chemicals in the mind, yet we find medications that are believed to rebalance these chemicals perform significantly worse if just taken alone without therapy to compliment it.
Personally, my theory on that imbalance just comes from you. It's hard to explain, but its your brain responding to the mental prison you have yourself trapped in, and the side effects of your brain responding to your mental state come back and perpetuate and negative mental state. Which is why, I believe SSRIs suck on their own, because essentially the imbalance is caused by something not physically tangible.
And we all crave it right? Happiness and what we associate ourselves with happiness. Everyones goals are different right? As in, what makes people happy. But ultimately thats what we all want right? Or more eloquently put, we dont want to continually feel like shit all the time. However, i think when we set out to achieve that in our minds, we start maybe asking ourselves questions like "what can i do now that would make me happier" or maybe any attempts to change their life will fall into a category of "will this make me happier", you get the idea. And such a focus on that priority actually hides the truth from us. What happens when we try to answer questions based on that target?
Well, we slip into things that makes slightly happier, but is comfortable. So binge watching something on netflix, games, maybe drinking/weed, eating. Then regret we made the wrong choice the next day but end up doing it over and over, instant gratification.
If we dont fall into that category, we find other routes make us even more unhappy because we feel like its achievable because of road blocks or just because its taking too long.
personally i found that, changing my priority, taking things one step at a time. You can restore balance and happiness. If those things aren't your targets. Something that really stood out to me was that scene in south park when butters was talking about how beautiful sadness is, because without it he wouldnt be able to appreciate the times when life was really good.
For me thats where I found balance. Day by day, step by step, I tried things that were just different. "have i done this before" "is this new" were my new questions. Some challenges were really difficult, and some days I turn off all modes of communication and retreat into myself. I didnt always like what i was doing. But eventually your life starts to become a lot clearer. You will learn things about yourself that no amount of lying alone in your mind could ever teach you. You will find things you like and more things you dont. And you will start building something out of that information.
Is it a cure? No. Does depression become more manageable? Hell yes.
I know how hard it is to make those first steps and how scary it is. Eventually we all will have to break free from justifying ourselves and actually start changing ourselves. Or we will disappear from history like homo ergaster who literally just thunk themselves to death.