It’s extraordinary how nobody of any prominence in aviation policy ever questioned BA replacing the 757s which were the majority of European route equipment in the 1980s-2000s with A319s of little more than half the capacity
BA introduced a policy of only 757/763 out of LHR on short haul, the still then newish B734s were banished to LGW. Nothing smaller than a 757 meant to maintain frequency, a lot more seats needed to be sold, as dropping frequency against LH/AF/SR/SN etc meant losing business travellers to the competition. However when EZY and FR arrived, there was no way of making money (over)charging hundreds of pounds to get people to Europe. So the idea was then to hang onto frequency, keep the business traveller happy and substatially cut down the remaining volume of economy seating.
The 757/763 was quickly reversed and a load of A320s were ordered as well as more A319s, as well as pulling in all the existing fleet out of BHX.