Originally Posted by RedTree
i was told by my an instructor I went to once because he was an OTTB he really only used one side which was his left and not really worked on the right when he raced...
But I don't really know
That is definitely a valid concern. I've never worked an OTTB, but from what I've heard and read that ingrained one-sidedness is a common retraining obstacle. However, the fix is the same as for a one-sided WP horse, or hunter, or eventer, etc: Evaluate the way you ride him and make sure that you aren't leaning or otherwise contributing to the issue; do lots of good bending, really riding him through the bend; look into an instructor or coach, knowledgeable eyes on the ground can be helpful in sorting out these kind of problems; and perhaps look into an equine chiro/massage therapist if there's a possibility that there is a deeper physical reason for the stiffness aside from being underworked on one side relative to the other.
Pro training experience has no bearing on whether or not a rider can affect the horse's balance and bend. Horses with pro training out the ears can be leaning, stiff, or bracey if the rider facilitates it, every bit as much as the average family/low level show horse.
Pics/video would be awesome!