The reality check is that Delta still flies 757 and a few 767s domestically (I get them all the time @
sfo) and has 21 A321s already (which blow away anything UA is flying domestically in comfort) and had another 121 coming. All of these planes are more comfortable than anything United is flying.
Yes, Delta has 79 737-900ERs, and another 51 on order,
but this is a fraction of what United has, and are old orders.
And while United is going with seats on the 772/77W that are .6" narrower per person than a 737, Delta is staying 3-3-3 on the 777, and is getting a fleet of Airbus with wider seats.
In a few years, on nearly every flight (the remaining 763/764, and the few airbus A319/320 with what we can all agree are the worst seats of any airline, being the exception) you will get a seat that gives you either 19.4" of width per person (the 772/77w) or 19.8"-20" per person (the 787, 737, and few remaining 757s) on United.
On delta you will get a wider seat: 21.1"-21.3" per seat (the A320/321s/763/777), 20.8in per seat (the A332/333/33neo), or 20.3" (the A350) on about 4/5 of Delta's fleet than what UA is offering.
The unmistakable truth is that Delta is very intentionally going with aircraft that are going to be more comfortable for passengers, and its part of a fleet strategy. People who can select what airline to fly will be able to take that extra about 1" per seat of width, and the better experience into account when comparing Delta to United.
