I am glad you're experince was positive, and even preferable to the local schools. I am also sorry that you're day school was horrible and glad you were moved to a safer place.
You are right that there are risks with any education or care setting.
I still think there are certainly children who are at greater risk than they would be at home, for some the disruption of healthy attachments, or the fact that you can't escape abusive staff or bullies at the end of the school day, the more limited comunication with parents can enhance vunrability.
This is not to say that children can not be in just as much risk or more in other settings.
But I do think it's good for parents to be aware of potential issues particularly around boarding school syndrome type difficulties and safe gaurding before they consider this form of education.
I expect also the risks vary from child to child and setting to setting, a very young and timid prep school age child, a child or preocupied parents, or who's parents are overseas and doesn't get home often or a child with comunication difficulties in a residental special needs setting may be more at vunrable for example than a confident 16 year old, who openly talks with their parents about any serious worries in an very well run senior school an hours drive from home.
My experience of boarding was certainly not positive, by no means the worse Ive heard of either. But I experinced or saw sexual harrasment, mistreatment, physical discipline, bullying and medical neglect. Their was very little privicy, education was poor quality, safeguarding and comunication with parents was lax.
Close to 30 years ago, not a big named school, but not inexpensive, a fairly small but well regarded one in a country house.