A specific back protector worn directly on the upper body always performs better than a back protector integrated into the jacket. Why? The protection fits perfectly on the part of the body for which it is designed and it stays there.
This type of back protector is often found on the track because of its protective qualities, but an additional reason is that your motorcycle clothing does not need to have an integrated storage compartment.
That not everyone chooses a separately worn back protector, is due to the fact that a protector integrated into the jacket already performs at a high level and that separate back protectors - besides being less practical - can be quite warm, especially in summer.