What a giant steaming pile of malarkey, the STUDY, just studied how many riders were at 10 percent. NO mention of where or why they came up with the 10 percent number. I think some of them might want to go actually ride a horse.
It seems to suggest that over 15% can lead to health issues according to the vet quoted, rather than just listing how many riders were at that size. 49% seem to be overweight according to them (more than 15%) and the only suggestion is that bigger riders need bigger horses - which is true but no mention of conformation.