Some people consider failure to be "completely unusable" - others say "if it doesn't repeatably track or return to zero - it's not working as it should - that's failure"
First group - says "my car burns oil, the passenger door only opens from the outside and there's a weird shimmy above 55mph but I get where I'm going and have been for 2 years!"
2nd groups says "it may work but it's still a chunk of chitt, this is better over here...."
For the person who buys a rifle to hunt deer with, a scope behaving imprecisely during zero is of no consequence. That shooter will get it zeroed and never dick with it again. That's not a failure, since the scope serves its purpose of allowing the shooter to kill deer. Then an internet blowhard comes along and insists that scope is a failure despite the fact that it does exactly what the shooter wants it to do.
Return to zero isn't just after an adjustment is made at the caps. It needs to return to zero after recoil.
Ideally - you sight in a rifle once and done. None of these mad rushes the 10 days before season to "make sure it's on" with a couple shots that turns into 6.
Rifles never should lose zero sitting in the cabinet. They lose zero or fail to RTZ after recoil AND turret spinning - should one chose to do so.
It is lost on some people that when comparing two scopes, one with an erector assembly designed and built to move correctly through lots of use (track, RTZ, etc.), and the other that moves erratically due to design and build quality, it is not unreasonable to expect the first to stay put more reliably than the second, as well as moving more reliably.
