Changing things to suit a horse better isn’t “letting the horse win.” They don’t know what win or lose is. They only know what works and what doesn’t. When they are learning, struggling, or worried, making things easier for them benefits us, too.
However, there is a difference between an adjustment and a crutch. The difference is adjusting to fit the horse is a temporary measure used to help them learn. A crutch is something you always have to do or the horse falls apart.