Yes, actually, as I've had occasion to directly deal with both of those airport managing authorities. Houston has some top notch airport managers (who have been amazingly successful, as evidenced by the airport's ability to attract a solid et of international carriers in recent years), while MWAA, well, is a maddening bureaucracy unto itself.

New United has adequate widebodies in fleet and on order, so that's a non-issue. However, much of the UAL capex spending over the next couple of years will be spent on the PMUA side to raise PMUA's domestic and international product offerings to PMCO standards. With the noteworthy exceptions of the longhaul F and C cabins, PMUA simply hasn't spent much on improving its hard and soft inflight products over the past decade, and refurbishing ~375 aircraft to install new interiors, AVOD, bigger overhead bins, and powerports ain't cheap.

Sure, both are single-aisle spaces. It is indeed hilarious that folks who move heaven and earth to sit in the single-aisle section of a widebody aircraft then gripe at the notion of sitting in the single-aisle section on a different aircraft, even when the seats are virtually identical and offer the same amount of space.