Yeah, I think that's the point of saying "unironic" instead of a direct antonym like "sincerely" - the latter connotes that the speaker might just be honest or mistaken while the former signals that there's a joke that the speaker isn't in on and that the only acceptable usage of the target term is an ironic one.
Yeah, I think that's the point of saying "unironic" instead of a direct antonym like "sincerely" - the latter connotes that the speaker might just be honest or mistaken while the former signals that there's a joke that the speaker isn't in on and that the only acceptable usage of the target term is an ironic one.