If iMessage were sending photos to the wrong people (even with extremely low probability) for over half a year, there would be serious negative publicity to App

If iMessage were sending photos to the wrong people (even with extremely low probability) for over half a year, there would be serious negative publicity to Apple for it, even if they had never implemented end-to-end encryption. Apple also has more software testers and more willingness to use telemetry. So while there are no 100% guarantees, I think the incentives are aligned with iMessage at least as well as they are with Signal. Apple suffered negative publicity from the 2014 iCloud photo leaks, even though those were "just" phishing and not a vulnerability/bug in the strict sense. Tim Cook had to give statements to the media, and in fact Apple stepped up its phishing protection by pushing two-factor authentication and notifying users about additional iCloud logins.