The OP only defines cannon as haveing 3-4 high output DD, healer and enhancer. Now assuming that taking a mob out very quickly (on par w/ mnk, war and nin as the OP mentions and as are considered in the minds of most "the" high output DDs) using 3-4 melee jobs, healer and enhancer it would seem that it meets the definiton of a cannon. Where otherwise a Pld, Rng, Thf, Blm, Brd and a Whm would not be considered a cannon, because that is going to focus more on straight tanking, skillchains, very controlled hate management and very determined party role.