Yeah, that's not how culture works, or ever worked. You don't need to be omni-dominant in a "large portion of the world". Most works of culture are seen, read, or heard by a relatively small part of the world, and they all contribute strands to a larger tapestry. Some strands are wider ("most influential") and/or longer ("remembered longer") than others, but every strand is part of culture. If you were to pick up a guitar and started singing at the local pub then that's culture too. No, it's not the reach of the Rolling Stones or whatnot, but that doesn't mean it's not culture.