Have you flown United recently? United seems to be on a fairly positive trajectory to me and for the last few years has been working to make the product more 'premium' and close some of the gap with Delta, the whole Dr. Dao thing seems to have been the low point but they were already rolling out Polaris lounges and improved onboard product at that point. The food onboard in Polaris when I did it a while ago was fairly poor but the rest of the product was actually not bad at all (I realise this survey is about economy).

I often think BA/IAG (and posters here by extension who stick to oneworld) have a somewhat warped sense of what the US market is because AA is their main benchmark. There's an increasingly large gap to me between i) DL and UA on one side which offer extensive international networks and not bad premium business class products and ii) AA on the other which is basically a domestic and LatAm airline that happens to offer a smattering of TATL routes on top. Look at the absolutely massive gap in operational performance and share price that has opened up between UA and AA over the last few years, AA is a bit lost as an airline, so I'm not surprised to see them in the bottom five alongside BA.