The reality is that during the time of 90's Trek there were never any official maps of the Star Trek Galaxy put out. They were kind of just making it up on the fly. So yeah DS9 does make it seem like all the major powers are located at least partially in the Alpha Quadrent. As far as I know we didn't get any official galactic maps till the 2000's, and they were just doing their best to make the haphazard and inconsistent geography of the Star Trek Galaxy make sense.