Traditionally the meaning of “backdoor” has involved intent as well as access. Unlike a basic bug, the system is working as designed but the designer wasn't trustworthy.
This is not true. A backdoor indicates that Microsoft is aware of it (and/or colluded to put it in), but there is no evidence of that. I respect your disagreement with my thoughts on how they should handle 0-days, but re-defining "backdoor" does not seem helpful.
By de facto, I was implying that they both accomplish the same things with almost the same list of pros and cons.
While I know there may be reasons to disagree with that practice, I think it would be a major stretch to say that it meant iOS suddenly had a backdoor.
The 0-day you were not reporting gave you escalated access to iOS devices. If Apple had given you a backdoor, you would have had the exact same access to the device.
Not saying its the same thing, which is why I used "de facto". The government just wants the access. Regardless the hole is intentional or unintentional, if a hole exists, then overall security is weakened
Many 0-days are built of of multiple bugs. A triple letter may use bug #1 and bug #2 to get a result, but another party will use bug #1 and bug #3 to get a similar result. Back to square one with corporate/government/personal equipment getting hacked reducing overall security.