Cost is king in BA now (and has been for some time). Right to Left on Long Haul saves the company a fortune. Why? Because the senior FO’s who are holding out for Long Haul command are pay frozen and junior bods go in as Captains on Short Haul thus artificially reducing the cost base on Short Haul. It is nonsensical to claim that right to left on long haul costs BA more, quite the opposite. There is no financial imperative for the company to change this one that is for absolute certain.
Plus in relation to Priam, realistically how many pilots ACTUALLY jump from fleet to fleet every five years? I would wager the number is relatively minuscule in the greater scheme of things.