The Gregorian calendar is by far the most commonly used calendar in the world, certainly in the English speaking world, and while I don’t particularly care to defend or attack your comment or the original comment, my point stands that the most obvious interpretation of what they said is in the context of the Gregorian calendar and to pretend they meant it outside of that context is silly.

The obvious meaning of someone saying “year 0 doesn’t exist” is that the Gregorian calendar does not have a year 0; the year before 1 AD is 1 BC. It’s not a math thing, it’s a protocol thing.

Your point on consistency is just wrong. There is no reason that “believing years exist” would necessarily imply “believing all numbered years exist”