Here is what the most recent running line of all Breeders Cup Classic winners looked like, after the mid-point (end of June) of their 3yo season.
They go in order from the winner of the most recent edition (Fort Larned) at the top through the winner of the first edition (Wild Again) at the bottom.
A lot of them obviously improved a lot.
Very few horses in history have great form as 2-year-olds, 3-year-olds, and older horses.
Even from the middle of the 3yo season on -- a lot of eventual BC Classic winners hadn't established top class level form.