BA's 'priority boarding' is a farce. Some flights have more passengers eligible for priority boarding than not, and shorthaul it is all called at once and often will still process the normal boarding queue in parallel rather than clear the priority queue. It really has become an almost pointless benefit.
Some flights have almost as many people eligible for pre-boarding when the half dozen family members for each person needing assistance are factored in as those eligible for priority boarding so yes it sometimes is a farce. But some airport gate designs (my home airport YYZ for example) make it difficult for there to be a fast track line because it only takes a few people to stand in the way because of the seating to make it impossible to get through so it's not totally BA's fault.