Yup, that's why as I said earlier...most kids you see riding are riding little PONIES, NOT mini horses...that's for a reason! Mini's were not bred to be ridden...driving is another thing altogther, but to be ridden...that's more for the ponies and horses that can safely carry the weight on their backs!
I had a mini X shetland For my 3yr daughter who needed schooling So I picked the lightest person I knew and trusted to help me out . My 15yr sis who weighed 50kg or 110pounds. Nothing major just flat work to get him a little more responsive as my daughter only weighed 16 kg at the time or 35 pounds . She was very tiny lol
So I agree that given the size of the people riding these minis it is cruel. And especially if they are unbroken . You would just jump on a 15hh + horse unbroken and trot them around if the mini could of thrown her off im sure he would of, So he was definitely bearing too much weight.