This is not true at all.
Some survive, but many die from the things you've described. Of those that survive, many fail completely to build a great life afterwards. They succumb to alcoholism, other addictions, and many die later from suicide.
Talk to any therapist and you'll find out that human fragility is the rule rather than the exception. After traumatic events, even those that "still manage to build a great life", as viewed from the outside, are often suffering greatly on the inside. Some of them manage to heal themselves with therapy and loving supportive relationships, but a great many don't. Which is why cycles of trauma unfortunately get passed on.
Certainly, I can be viewed as stereotypically successful by my buddies. Certainly, because the mask we wear should be strong and never come off. But in my nights alone, or even in my therapy sessions, who could possibly see that 'me'?
I have come to realize, though, that most people who didn't suffer much, refuse (implicitly, not explicitly) to empathize with those who have -- perhaps even I may be included in this group which 'refuse implicitly' at time. It's not that big of a deal, though. (Generalized) Empathy is a difficult skill to train.
The way you say 'look at all the people' implies that a lot of people survived and had good lives, but this needs to be weighed against the number of people total that entered concentration camps to know if this is actually a meaningful number of people to validate your assertion or not.
My guess is that someone who went into a concentration camp were much less likely to live a life worth living than people who did not simply because a large number of them lived a life of torture and then death.
That doesn't mean that such factors don't DRASTICALLY reduce the odds of this happening. Moreover, some people being able to build a good life after such trauma doesn't mean that said trauma isn't a hinderance.
I don't think we're claiming life isn't "worth living" after adversity. Just that it's somewhat obvious that they will make similar mistakes due to the challenges they face, at least more frequently than those who do not face such adversities.