There is no training a horse to be TB, they either are a Thoroughbred or they are not. Just because a horse has parents that could route doesn't mean the ofspring will route, they may be sprinters. And if they are going to run a route, they all start with shorter races. You can't get a horse properly fit for a mile+ race for its first race, and even if you could, that's a long time to be focused on something they have never done for a baby.
I agree but StormyBlues stated she knew more than her trainer so I didn't want to state the obvious.