The only universal truth is that no thruths are universal. And I think “suffering builds character” in this and its other forms is a perfect example. Yes, extreme suffering will cause long term problems. And yet at the same time, we’re all probably familiar with or know someone who experienced “the gifted student wall” where their natural talent was good enough to carry them to success, right up until the point it wasn’t and they suffered a major setback because they’d never built up the skills or resiliency to overcome that obstacle.

Like you said there is probably some sweet spot that we should try to hit. I suppose the hard part is there’s no good way to know how much suffering society should allow or encourage, and probably more importantly no good mechanism by which we can turn off suffering once you’ve “had enough”