they've had an opportunity to raise their standard against competitor's offerings
It appears that the ambition of all large monolithic organisations, eg retail banks as well as BA, is to not be worse than any competitor, rather than to be better than any competitor. How often have we been told; "Well, it's just the same with all the others, you know." The inevitable consequence of this mindset, which I'm sure is taught to MBAs as the right way to approach the subject because it's the least expensive, is a depressing downward spiral of mediocrity.
That's the way it is...
Ah, the "twaz ever thus" response.
It does not have to be that way. It can be better, but only if everyone simply refuses to accept it, makes trouble, is rude, loses their temper, and generally behaves badly when confronted with appalling service and attitudes from those who take your money. (Sort out the grammar in that sentence if you can.)
BA do not have staff sitting around waiting to be called in for such an event
Oh yes they do. They're called managers, off-duty staff, temps, whatever it takes to get things done. If a manager cannot do the job of everyone under his or her control he or she is by definition useless. Planning for such emergencies means practising for them, training the extra staff, whatever it takes to provide a good service. Massive disruptions to flights happen regularly and there is no excuse for not being prepared to deal with them properly.