I suggest you familiarise yourself with the basics of research in psychology.
Much of the research on the matter doesn’t simply highlight instances of trauma, as you suggest it does. It starts with a representative sample of boarding-schooled children and establishes the proportion of those who have suffered trauma. Therefore, it does take into account children “who had a nice time at boarding school”. Then, it unpacks the nature of that trauma among those who suffer it.
Sure, there are some children who “had a nice time at boarding school”. I agree with you those children exist. But, a significant proportion of boarding schooled kids, as demonstrated by research, suffer mental trauma. That is why boarding schools are a cause for concern and that is why I started this thread. There are many activities in life that damage some, but not all, of their participants, and we deem that cause for concern. Boarding schools are no different.
As for “personal experience’, my personal experience is reading the research literature in an objective manner. One person’s lived experience - in this case, yours - doesn’t negate any of that insight.