>Your definition of "common" is out of step with most people's.
This is uncharitable. Adjectives can be extremely contextual, and "common" is very much one of those words. The biggest factors are relativity to other things in the same domain, and deviation from popular perception. E.g. if most instances of X in a given domain are ~1 in N, people will generally use words like "common" and "unusual" for Y if it is greater than or less than 1 in N, regardless of what N is. Or say Y is exactly 1 in N, but people at large misestimate it at 2 in N. Now you might say it's "rare" despite whatever its relativity to the domain is. Now note that X and Y usually belong to effectively infinite domains, throw in the ambiguity of conversation, and it gets very fuzzy. This is basically a long way of saying that this is a semantic argument, and therefore may be divorced from the original implication of the adjectives being contested.
This is uncharitable. Adjectives can be extremely contextual, and "common" is very much one of those words. The biggest factors are relativity to other things in the same domain, and deviation from popular perception. E.g. if most instances of X in a given domain are ~1 in N, people will generally use words like "common" and "unusual" for Y if it is greater than or less than 1 in N, regardless of what N is. Or say Y is exactly 1 in N, but people at large misestimate it at 2 in N. Now you might say it's "rare" despite whatever its relativity to the domain is. Now note that X and Y usually belong to effectively infinite domains, throw in the ambiguity of conversation, and it gets very fuzzy. This is basically a long way of saying that this is a semantic argument, and therefore may be divorced from the original implication of the adjectives being contested.