This is getting finnicky, but generally I would consider a quality issue to be something to do with the build (ie substandard materials, poor riveting, trash in the dead spaces in the walls - as has been alleged on the 787) as opposed to what happened, (in my view) which was cost cutting - as you point out, they basically tried to do a software emulation of the previous 737. The issue isn't flight worthiness - the 737 MAX can be a safe plane - but they cut costs by not wanting to do a recertification or retraining. I guess that is a quality and safety issue, but not what i'd normally consider quality?