While as a software person, I agree with you in principle, Apple (what’s their market cap these days?) still looks bad no matter how you slice this.
The way I see it, this is not like testing a large number of possible user interaction permutations as you would with an app. In this case user interactions end the instant the user clicks a button to initiate the install.
While there are multiple combinations in the way of upgrade paths, these should be well known and documented for any given supported device. Same with the set of supported hardware configurations (memory, 5G, etc.).
If, for example, it turns out to be something more obscure, like a specific combination of system Settings, that’s still on Apple to document and include in their test procedures. If we find out there is a hardware defect in some iPads, again, Apple blew it.
Some people paid a premium price for a device and are being inconvenienced through no fault of their own. I guess I just don’t get the urge to ask for “understanding” on behalf of the multi trillion $ entity that is ultimately responsible.