I agree that most problems young adults have are results of traumas in their early childhood that never have been properly processed and only once you realize this and resolve them you have a chance to find mental peace.
I don't think you need severe stress in order to grow. Stressful situations are nearly always a result from a emotionally distorted perception of reality. By this I mean that a "grown" person wouldn't perceive these situations as stressful. The stress comes from an overdramatisation of the situation in the brain.
I think that good parenthood can give a child the security even from early on that it does not feel stress in challenging situations.
But yes if you are already fucked up experiencing stress and experiencing how trivial those situations are in reality this might be a good teacher. But if you are too stupid or damaged to learn from those situations they will fuck you up even more.