As a long-time breeder I pride myself in producing healthy and sound youngsters. By the time they go to their new owner I will have already done a preliminary vetting to include x-rays because I don’t like surprises and prefer to deal from a position of strength, if you will.
In my opinion, when you have a 3-year old youngster with good radiographs and sound movement, it is up to you to continue managing this animal in such a manner to where injuries due to overly stressful training are avoided and you continue to build up the muscling and endurance required for your discipline.
That does not mean that “stuff won’t happen”, but your horse will have the correct “foundation” to deal with the occasional “over-stressing” that is bound to happen during its career.
I believe that breeders can only control the environment their “product” while it is at their place, and that injuries incurred during competition years should not be attributed to bloodlines but rather training practices and/or bad luck
Just my opinion…