I’m sure we have all been in similar situations and yes it is very frustrating.
My local airport is a BA outstation, and when on one occasion the aircraft went tech, it did its utmost to resolve the problem ASAP. At Heathrow a replacement aircraft would have been found very quickly.
Why do I continue to fly BA? Well, it’s the only airline that flies from here to LHR and its Executive Club is in my opinion the best out there.