I'm not sure it's much of a problem. Indeed, it reflects some realities: cities at major junctures, like ports and borders, often exercise important political and diplomatic roles despite their size and being on the periphery would suggest. Being at the wormhole makes DS9 more like Istanbul or Strasbourg or El Paso, places where high amounts of traffic bring with it other types of non-economic activities. Moreover, the emigre communities in these places tend to be regarded as resources to their mother countries. A bartender might normally be a bit player in political affairs, but being on the station may be enough to significantly elevate Quark's stature.