UA is in a tough spot having direct or indirect competition at nearly all of its hubs.
Direct or indirect competition, so said differently, they have competition within their hubs... does any carrier not
have that issue?
compared to DL & AA pretty much all of UA's hubs have large competition whether in the same airport or a competing airport.
ORD- AA hub there, and WN at MDW down the road
IAH-WN at HOU across town
IAD-AA at DCA, WN at BWI to a lesser extent
EWR-B6/DL/AA at JFK AA/DL at LGA
LAX-DL/AA/WN all have large or equal ops
SFO-WN at OAK across the bay
DEN-WN & F9
Delta is probably the best at having fortress hubs. ATL even with a hundred and so WN flights DL is such a behemoth at about 900 daily flights it rules there.
MSP & DTW have about 400-500 flights whereas the next largest carrier probably has 20/30 some flights. SLC basically the same 300 flights vs the next largest carrier. DL owns their main hubs.
American is also somewhat good with fortress hubs. CLT being the main one with nearly 700 flights up against DL which probably has 30 some flights. DFW is kind of the same boat like DL at ATL...while the do have WN across town at DAL WN until recently has been hamstrung there and will always probably have some constraints whereas AA has 800 flights. After that they kind of deal with the same issues at LAX up against UA/DL/WN, PHX has WN to contend with, ORD has UA. DCA they probably get the nod there since its the preferred airport and they are probably actually bigger than UA at IAD.
UA(CO) at one point had IAH at a fortress level with over 700 daily flights but that has shrunk substantially (I think down to 500 plus or minus--a big drop off for sure).
I still think UA's best bet to serve the Southeast is a combination between IAH & IAD. They geographically touch the fringes of the region. IAD in particular could be utilized more, but they go up against DL which pretty much owns the region and always has and AA which is the next biggest (vis a vis US and PI before that). People in that region are just used to going through either ATL or CLT.