I’m sure others have said this, but finding a saddle for the horse is about knowing a horse’s shape and what types of saddles fit best with those shapes.
IMO, finding a saddle for the rider is less about finding one that people say is secure, but finding one that works with the rider’s conformation. The saddle that put the rider in the appropriate position will always be more secure than one that doesn’t. I see so many people wanting a deep seat and calf skin because it’s secure…when you can have a flat, flat saddle with the grain leather that is the right balance and the rider will feel infinitely more secure. It’s a combination of twist, seat, flaps, stirrup bar placement, etc.