Why do so many serious dressage riders I know dare not take their horse on a trail? Is it because those horses do not have the makeup to be safe on a trail?
Problems with a horse are not fixed because we want them fixed it. For things to change with our horse it must begin with things changing with how we work with our horse.
A horse is a brain on four legs. A horse is not a body with four legs. If you want a horse to do anything you should have a conversation with the brain.
My take on this concept is that when a horse is first started, having a job to do can assist a horse to get comfortable with just carrying a rider and following some direction.