"I can't imagine a way for this feature we advertised to actually work" is not an excuse for false advertising! But there is a way to do better. Google's Android backup is E2EE by default. It does not require remembering a long password. All it requires is your phone unlock code, which you normally enter at least once per day and are extremely unlikely to forget. This is actually how Apple's works too, when ADP is enabled. Either it should be enabled by default or Apple should stop claiming iMessage is E2EE.