That is interesting about leather ones breaking more easily. Being so nostalgic for old ways, I always wanted a leather one. But my rider education didnt allow for collars and bridles to break. In my lessons, a horse that ran away was supposed to go with its bridle or head collar on? And even the lead rope.
I was taught. Meaning I learned to ride as an older adult. My learning involved learning how to lead a horse. And later teaching a horse how to be led. No RI ever used or spoke of using a collar or bridle that would part. For our safety we were taught to let go if a horse ran. I am not saying you are wrong. Just that my horsey education did not include the suggestion that a horse might be injured by its collar . I have ridden 13 years now and led horses to and fro on roads and tracks and never saw any incident . But this is urban London. It is easier for police and passers by to grab a loose horse that has a collar on. The main danger to loose horses here comes from fast moving traffic.