In my experience, you can weaponize processes like the Five Whys or the Amazon Leadership Principles. I don’t think that means they don’t have any value.
That being said, in this case, I agree with your manager. Both the QA team and your team had fundamental problems.
Your team (I assume) verified the functionality which included X set of changes, and then your team made Y more changes (the flag) which were not verified. Ideally, once the functionality is verified, no more changes would be permitted in order to prevent this type of problem.
The fundamental problems on the QA team were…extensive.
That being said, in this case, I agree with your manager. Both the QA team and your team had fundamental problems.
Your team (I assume) verified the functionality which included X set of changes, and then your team made Y more changes (the flag) which were not verified. Ideally, once the functionality is verified, no more changes would be permitted in order to prevent this type of problem.
The fundamental problems on the QA team were…extensive.