UA carried more passengers than any other carrier in NYC area airports last year, so maybe not a total shortsighted decision. Also, from a logistic point, JFK had only served TCON flights at the time of operations transfer - nightmare scenario for transit pax.

Again, FT is not representative of the public flying demographic. UA took a much PR hit after Dr. Dao; in comparison, all of these changes are walk in the park.

While technically in the city limits JFK is not near Manhattan which is presumably where many of those high dollar customers are headed. The whole "it's not NY but NJ" is a marketing issue. Logistically EWR may be the best option depending where you are going.
The biggest issue I see is the lack of connectivity to the other *A flights out of JFK. I was looking at an itinerary next year with a flight on LX but it would have had me connect from JFK to EWR which although feasible is not something I would have much interest in doing.

Yes, but didn't some *A flights move from JFK to EWR in response to UA moving out?

I can't speak to that as I honestly don't know. I know there are still a lot of *A carriers at JFK (LH, LX, CA, LO, CM and others) and unless their traffic is O/D in JFK (a possibility since it is NYC) their pax would have to trek to EWR for a connecting flight on UA.

No, as passenger would not need to trek between EWR-JFK for a connecting flight because of a lot of redundancies in the *A network. All *A carriers at JFK also fly to another UA hub, so a US passenger can easily bypass EWR/JFK.

There are very few routes at JFK that *A flies to and not covered by any other hubs: LO BUD/KRK-JFK, ET ABJ-JFK, AV CLO/MDE-JFK and EW DUS-JFK (which is seasonal). I left out LX GVA-JFK because JV would make it metal neutral on UA EWR/IAD-GVA.

I think it's both actually.

They lost people who live on the East Side of Manhattan, in the outer boroughs, or on Long Island, and they lost people whose connecting international flights arrived or departed from JFK. They retained and strengthened their monopoly power at EWR, however, and also enhanced service for their customers on the West Side of Manhattan, in Lower Manhattan, and in New Jersey.

The thing is, JFK has both slot and gate shortages, and if you are going to run service out of there, you have to run enough that you can actually have some plausible connections to international flights. So while you may not need a hub like DL, AA, or B6 has, you at least need flights to each of the United hubs (LAX, SFO, DEN, IAH, ORD, and IAD) and then also to some other popular destinations like Miami and Seattle and Atlanta. And once you do that, you are flying on routes that are ultracompetitive and the profits are going to be very low- and you are also never going to be able to offer the frequency or convenience of connections that the competitors offer.

So in order for a UA operation at JFK to work, they would need (1) more slots and gates than they had, and (2) to run a number of routes that may be unprofitable. It's not impossible for the thing to work, but I understand why they retreated to EWR.