]Efficiency and reliability are obviously not the same. I have no idea of what all to expect with the longevity and reliability of heat pumps but if it is anything the ridiculously steep decline to complete unreliability with refrigerators over the past 10 to 15 years, that obviously needs to be considered as well.]
Case in point being a low-end 20-year old working Procter Silex toaster oven I discarded for a newer one, and the 3 toaster ovens that have failed at 3 year intervals since. They used to have 90 day warranties and worked until you threw them out 20 years later because you got fed up with the baked in grease stains. Now they warrant them for 1 year, but they die after your extra cost 3 year warranty expires.
Your explanation may have some merit but I think that much of the unreliability relates to the design complexity that has been forced on the manufacturers and the fact that more and more is being crammed into less and less space. Case in point... how many examples does one need in the automotive industry of new regulations being forced on to the manufacturers that a) quite often don’t meet any of the original objectives and b) ultimate cause nothing but grief to the owner? For the pickup truck that I bought that had 4 to 8 cylinder AFM switching capabilities, did that do anything to increase the life of my vehicle? Of course it didn’t... caused all kinds of injector and other problems. Well, just look at that principle as applied to stuff with refrigeration cycles...