I think the breed is different today, and while there has been dilution, at the same time the horses of today are bred for more and easier speed. Today breaking yearlings is simple, they are mostly broken already, LOL.
Look back in the 70's and where leading stallions came from. Look at the 80's and the 90's. How many stallions did Bill Robinson make---taking into consideration the # of top horses he had? I think it's easier to make a stallion today---not necessarily a good one, LOL---but in the long run, the breed is getting diluted.