Supplements, like glucosamine, cannot be digested through the horse's intestinal track and therefore do nothing. As long as the horse has the correct building blocks for strong ligaments, tendons, suspensories and muscles like amino acids, protiens, fats, etc. and is conditioned correctly to build strength in them, they will be strong.
Top horses are rarely on oral supplements and are usually on a rigorous course of IM Adequan (up to every day or two days), with Legend and occasionally Tildren.
Horses with chronic lameness, bad injuries, poor conformation or bad joints rarely make it to be top performance horses. So no, I have not had soundness issues with top horses, nor people I know. And if they have, the horses were almost immediately retired.
They say money doesn't buy happiness -- well happiness doesn't buy horses!