Success is the best antidepressant. Weight loss does wonders.

First, everybody should have financial security - it's better not to have justifiably pissed off desperate members of society.

Next, everybody should have decent healthcare, physical and mental - society is not stronger having weak / broken members.

Then: people are still going to be depressed. People who have all the financial security, access to all the best therapy, no "real" problems in their lives still get depressed - like: Carrie Fischer suicidally depressed. She's not an isolated case. Some of it's genetic (runs in families), some of it's environmental, some of it's just mental. Most of it's based in feelings of hopelessness / helplessness. The AA serenity prayer is very applicable:

...grant me the serenity to accept the things I cannot change, Courage to change the things I can, And wisdom to know the difference.

Genuinely internally actualizing those three things alleviates a lot of depressive feelings. Not everybody can do it on their own, even with support many people still struggle. It's likely underreported, but globally 1/100 deaths are ruled as suicides. Among ages 15-29 it is the third leading cause of death.

But if that was true Elon would be the happiest person on earth.

That should just be the bare minimum for everyone and whatever other issues can be handled by therapy, but instead we live in a world of constant, easily preventable trauma and the ones who have it the worst have the least access to therapy. Great system!

Having financial security eases with financial worries to an extent but doesn't entirely solve even that issue nor does it even begin to deal with the unrelated issues. One can be financially secure and absolutely miserable.