Ok I'll expand. Some parts of the GQ might be more than 70 000ly away. But at it's closest point to Bajor the GQ is far closer than 70 000ly away.
But Sisko obviously wasn't referring to the closest point, he was referring to where he was at the moment -- "over 67 years to get here
." Sure, he was speaking a bit imprecisely, but even I wouldn't be that pedantic about it.
, I agree -- the Federation and its neighbors are called "Alpha Quadrant" powers even though many are in the Beta Quadrant, in the same way Europe is considered part of the Western world even though most of it is in the Eastern Hemisphere.