If this thread is focusing those living in the District of Columbia or in the north Virginia area within the same proximity as those in DC, then I think there is no debate that one should just choose the airlines flying out of DC to those selective destination served directly by those airlines. There is not much of debate.

But those who live in the greater DC Metro, there may be greater population who prefer flying out of IAD for direct domestic flights and for international destinations. I would think the population of greater DC Metro area is likely a better sample than just those living in the district or DCA surrounding areas of VA.

I can also pinpoint those I know who live west of Tyson and north Bethesda who find a hassle going all the way to DCA much like those who lives in the district who feel about traveling all the way to IAD.

There is demand for both airports independent of UA loyalists. I would say there are more UA loyalists living outside of the DC than inside the District itself in the greater DC Metro area.