Logic not a strong point of mine, but after you have spoken of your disapointment of BA and of LHR, maybe you could try another UK airport?
They all seem just the same, well the ones I have used any way.
This morning I was dropping a friend off at Boston Logan and sat drinking my coffee watching security. Approx. 50% of people trying to pass had to be sent back due to failing to read the notices, ie failing to remove coats or to empty pockets or belts etc..
Wait time about 5 minutes, number of flights 1. Compare that to T5.