You're using the wrong standard. The standard is not "perfectly fair" it is "significantly premined."

CMC seems to think that an instamine of 35% in one day counts as that. I think they should clarify the tag and make it "significantly premined or instamined", but that's up to them.

I disagree with your statement that instamined doesn't have a clear definition. It has a reasonable common sense definition and plain English definition that means "mined extremely fast" just as "significantly" has such a definition. I don't know what criteria CMC uses for "significantly" though.